Hm, where do I begin...
I was very late to the party so to speak since I bought Total War Attila relatively recently.
Now I realized that many factions (especially Poland and Teutonic Order) could probably use some improvements but I don't know if you're still working on those specific unit rosters or not so I'm not sure if I even should post about it tbh.
Anyway, here are some sugestions about Polish unit roster:
All tiers:
Firstly, the mounted sergeants. The idea of "sergeant" sounds a bit... off for a medieval Poland. I would suggest changing their name to simple and more accurate "retainers". That would fit way better.
Tier 2:
Pavise Crossbowmen: As far as I know tier 2 is supposed to represent the time frame between years 1300-1400. If so then it is too early for the appearance of pavises in the Polish Army. Despite the fact that the immediate neighbors of the Kingdom of Poland already used pavises (like Prussians, Teutonic Order, and Lithuania) Poles didn't adapt them till the early 1400s. My suggestion would be to remove the "pavise" part of their name and replace their pavises with some regular triangle shields. That way the balance will stay the same while improving the historical accuracy a bit.
Pavise Spearmen: Same as Pavise Crossbowmen, maybe call them "Spear Militia"?
Lithuanian Archers: I'm not sure what to do with this unit. One the one side, Lithuanians actually rarely gave any military support to Poles and with exception of the Great War against the Teutonic Order Poles and Lithuanians almost never fought side by side before the end of XV century, on the other however I'm not sure what other unit I could suggest to keep the balance and don't make playing Poland boring. Maybe change the name to Ruthenian Archers instead? (the Kingdom of Poland owned Ruthenian lands). That way it would be a bit more historically accurate.
Lithuanian Cavalry: Same as Lithuanian archers, their name could be changed to Ruthenian Cavalry instead. It would make much more sense.
Heavy Axemen: They aren't historically accurate either but I'm sure you knew that already, I bet you guys implemented them for balance and to make gameplay fun so I won't be complaining especially that I have no idea for a replacement.
German Men-at-Arms: I'm not sure about that one. I don't think that Polish kings ever made extensive use of German mercenaries at the time. Most mercenaries in Poland were usually of Silesian, Czech (like Jan Zizka himself), Moravian or Hungarian origin. Not only that but Holy Roman Emperors did once or twice outright banned German knights (Bohemians didn't give a s....t) from providing their services to Kings of Poland as they most of the time fought against Teutonic Order. Maybe changing to just "Foreign Men-at-Arms" or even "Bohemian Men-at-Arms"? I don't know it would be mostly cosmetic so I live it up to you.
Tier 3
The times represented by Tier 3 were a time of swift transition in Kingdom of Poland from using feudal armies to professional ones. It would be nice if the roster would reflect that better. It was also a time when Polish armies adopted the use of wagenburgs (wagon forts).
Pavise Spearmen: Although Poles started using pavises and professional Men-at-Arms in XV century I don't think any of the surviving rolls ever mention a single man-at-arms using a combination of spear and pavise. Instead, most of the pavisemen (outside of crossbowmen and handgunners constituting about 70% of all Polish infantry) were armed with swords, messers and sabres. So my suggestion would be to change them to "Pavise Swordsmen" and as the name suggests equip them with a combination of arming sword and pavise shield. I guess levy pavise spearmen should be left out for balance reasons.
Levy Halberdiers and Halberdiers: There is one little problem... During the whole medieval history of the Kingdom of Poland halberds were NEVER used. The closest area were halberds were in popular use was Silesia which at that time was already a part of the Kingdom of Bohemia. And as shocking as it may sound there are virtually now archeological findings or written sources that could confirm that halberds were ever used in Poland before the beginning of the XVI century. They do appear, although rarely in iconography but exclusively in hands of "bad guys". If you are not aware of this, in medieval iconography there was a trend/rule that weapons that appear foreign were often given to the characters representing "bad guys" in any given scene. There is a term for that in English historiography but I just can't recall it.
I think it would be a good idea to change them to Levy Voulgiers and Voulgiers respectively which should be easy since they are already present in the mod.
Levy Pikemen: Now, this is problematic as well since pikes have seen barely any use in Poland before the second half of the XVI century. I didn't mention it in Tier 2 since I had no idea how to replace them in the years 1300-1400. There are certain ways to go about it in the time period between 1400-1500. Namely at the turn of XV and XVI century, the new type of infantry was introduced into the Polish Army. Kopijnicy - literally Lancers. The name may cause some confusion since there were two unit types of this name in Poland, one being a type of heavy infantry and the second being a type of heavy cavalry which was basically a Polish equivalent of French gendarmes. One, however, wasn't a dismounted version of the other, they were two separate things.
But, back to the topic. Said Foot Lancers constituted about 10% of Polish infantry. They were equipped with full plate armours, long spears, and longswords as their side weapons. But with time pikes also got more and more popular I will put a fragment of the painting depicting the Battle of Orsha (year 1514) in the spoiler. You can see the foot lancers in the first row of infantry and at the bottom
Since the pikes in the mod aren't that long, to begin with, I think you could replace the tier 3 pikemen from Polish roster with Foot Lancers and since most of the time said foot lancers were also NCOs you could call them Pikemen Sergeants for simplicity. Although I would advocate using the name Foot Lancers.
Heavy Axemen: Once again, a unit that appeared in tier 2 already but I can't think of any historical replacements. In Tier 3 however, that could be replaced with Flailmen. Yes, Flailmen weren't exclusive to Bohemian Hussites. Later Polish Kings were recruiting them too, either from Bohemia as mercenaries or from local men. I know implementing actual flails in the engine would be a nightmare but from what I remember you guys went around it and simply equipped Bohemian flailmen with two-handed maces. I think flailmen should replace heavy axemen. They can be equipped with armour since in Poland they weren't some peasant volunteers but professional soldiers.
German Men-at-Arms: At the beginning of my "evaluation" of Tier 3 I mentioned that the XV century in the Kingdom of Poland (like in most of Europe) was a time of transition from feudal armies to professional ones. I don't think that German Men-at-Arms fit here at all. At the time mounted Man-at-Arms or "Lancers" were mostly recruited from Polish Nobility. Germans, just like Czechs, would mostly find their way into Polish infantry. So I think that this unit should be changed into simply Men-at-Arms of Lancers and be a better version of regular feudal Polish knights (since they would be more disciplined and trained to use more complicated formations and maneuvers).
Sources (most of them):
A. Nadolski Polska technika wojskowa do 1500 roku (Polish military technology up to year 1500)
A. Nadolski Grunwald 1410
j. Sikorski (and many others) Polskie tradycje wojskowe. Tradycje walk obronnych z najazdami Niemców, Krzyżaków, Szwedów, Turków i Tatarów X-XVII w.(Polish military traditions. Traditions of defense struggles with the invasions of the Germans, Teutonic Knights, Swedes, Turks and Tartars in 10th-17th centuries)
M. Bogacki Broń wojsk polskich w okresie średniowiecza (Weapons of the Polish army in the Middle Ages)
That would be it for now. Depending on how useful you'll find my feedback then I can post some more info about the Teutonic unit roster and other Central-Eastern Europan factions. I know you guys have to find a balance between fun gameplay, historical accuracy and well... balance. I'm not pushing since you already have to put a lot of work in the mod and might find changing already functioning army roster redundant as it could more work than it is worth. Anyway, good luck with your work.