When we look at TW mechanics and the whole sword>spear thing, problems arise, when trying to balance this somehow. Older games in the series like Medieval 2 are harder to mod in terms of unit function. I see many people try to make weapon options for units different in some way, but its mostly the attack aspect. My idea is that if you want to make things more accurate, you should not look at attack alone. Defense should be considered as well, because different weapons had different strenghts and weaknesses. Here is what i think how weapons could be balanced.
One handed weapons. Mostly used with shields, so this is a harder decision.
Spears and swords. Spears are the kings of all weapons, but like everything, they have downsides. The main strength of the spear is that its a very balanced purpose weapon. Its easy to use spears in civilian or warfare situation. Most of the time, spears faced less armored opponents or without armor at all. Cut wounds were ugly, but puncture wounds were deep and deadly. This means that if you do manage to stab someone, its gonna be bad day for him. Its not easy to pull of, but with the reach of the spear, you can do it safely and that's the point of spears at least in battles. Now to start comparison of spears against swords, we have to look at the biggest downside of spears which is armor penetration. Yep, you read it right, spears suffer against armor, hear me out. Despite many spears being pointier than many swords, it is still not easy to face armor. It all depends on the armor and the coverage of your opponent. When looking at armor like mail, its protectiveness depends in things like ring diameter (tighter weave), ring thickness and the pattern (like 8 in 1, which would be more rigid, probably not used for body armor, but lots of usage for things like throat protection). All these variables mean that you are either going to put more energy into your spear thrusts and try to penetrate the mail or create blunt force trauma by doing so, or you will be trying to aim for the weak spots, which will be much harder and your opponent will know his weakspots, how to protect them as well. Contrary to popular belief, mail is not that weak against penetrating force. Even the riveted mail, which is tested nowadays is mostly indian, has poor riveting, not historical. You can go and see tests done by people like Thegh Thrand and see that it is the rivet that fails, not the ring itself.
This is indian-made mail. Cheap, works. Not that historical, there can be some improvements made. People use this for tests and yes, it is riveted mail, but its just riveted badly.
This is historical mail. Notice how tight the riveting is. Much better. Made to protect, not to cut costs. This would protect much better against spear thrusts.
There are videos that show riveted mail being tested against various types of weapons and there are a lot of comments in them saying "oh finally, some riveted mail. im so tired of people testing on budded mail and stating that it suck." This is true, testing butted mail in context of Europe is not historical, its better to test riveted mail. The thing is, riveted mail can be also unhistorical and if its made in modern times and riveted poorly, its still not a good test. Here are examples of such tests. Notice that the part, which usually fails is the rivet, not the ring.
https://youtu.be/ydjdBTV8ZbY?t=185
https://youtu.be/JqkiKjBQe7U?t=1059
Now back to spears vs swords. Like i mentioned before, the problem of spears is the lack of anti-armor capability, but this is where swords come in and its funny, but i will explain. Swords on paper are worse weapons than spears. They are even worse against armor, mostly, they have less range, they can thrust, but if you want to cut, you need more space to do so. For civilian combat, its not a problem, but we are talking military here. Even though swords have these problems, compared to spears, they are still versatile weapons. They are harder to manipulate than spears, mainly because of shorter length. This means that you can protect yourself more easily with a sword and the fact that the weapon is made out of metal will mean that you are going to have more reliability in the long run. When facing armor of any kind, this is where swords shine. You can't have initiative in terms of attack, but you can wear your opponent down. I know this is a bad example, but look at the battle of Visby. Yes, knights and professionals fought militia, but how they did it brings attention to how swords were used against armor. Gotland militia are confirmed to wear standart amount of body armor for footmen, which means that almost all of them had unrpotected legs. Skeletons of battle of Visby show ridiculours amounts of cuts that people received to their legs, mainly shins. Those cuts were so light that sometime shin bones have more than 10 cuts with or without the final cut, cutting off the leg and finishing the fight for that person. This really shows how you would use swords against spears. Try to bind spears, manipulate them and then make a cut as fast as possible to a weakspot. It won't kill your opponent, but you will be safe and he will be hurt. Do this enough times and you win the fight and hopefully - the battle itself. Visby, of course, is an example, where superior force defeated an inferior one, but i think it can still be used for argument.
Some interesting points, made in the documentary of battle of Vsiby. https://www.youtube.com/watch?v=TxkgBDaVsP0
Now onto axes and maces, just very brief. Blunt weapons are really more simple, they will bonk people regardless of the armor they are wearing, but are more suited for use against armor. We know that axes are better cutters than swords, but they lack the protection and reliability to hit things. You have a small portion of the blade on your axehead, compared to larger blades of swords, yet if you manage to make the cut, its devastating. Not all axes are the same. Broadhead axes are made to work against unarmoured opponents, while smaller, wedge-like axes are much better against stiffer stuff like armor. Some axes like czekans are really similar weapons to warpicks, they even share the name with them in some languages. Eastern cavalry axes are the same thing, they did have a pick or a hammer on the other side, so they were hybrid weapons, not just axes, that should be taken into account.
These are lake Lednica axes. They have thin, light, broad heads made to cut mostly unarmoured or textile armoured opponents.
These are khazar axes, made to concentrade a lot of energy in small area and with their wedge-like distal taper, they will have lots of splitting power. Perfect for horseback use.
These would be very good ideas for one handed weapon balance, yet only for foot soldiers.
Spears: Good for everything. More melee defense. Of course has more range. Also is the only weapon good for charging on foot, so more charge bonus as well. Decrease in unit price.
Swords. Good for prolonged combat. Unit has lower damage, but very high melee defense. Increase in unit cost.
Broadhead axes. Highest unit damage, but no defense bonus.
Anti armor axes, warpicks, maces and other blunt weapons in general. Just has armor penetration, no other bonuses.
These are just ideas, don't take this seriously. Its just something i am passionate about, so i came up with it considering the realism and game mechanics into account.