Here's the reasoning behind the first idea.
In history, battles were usually over after lower casualty numbers than what we get in PB battles at the moment. I don't remember an example of the loss percentage in battles of this era and region of the world, but it seems the creator of a similar
mod, Cesco, has done some homework on the issue:
"These changes are based on the observation that during ancient battles a really low number of men died during combat, while they were mostly killed by cavalry when they routed: winner army had a small percentage of losses (5-10%), while the loser one suffered about 30-50% of casualties."
If you remember my first battle report for RB, I found one slinger unit down to 10 soldiers but still fighting: what's the loss percentage of that without yet having been broken? And this with the losses after the collapse still to come. Other units in my battle, like some melee units, broke at lower loss percentage than that, probably because they were surrounded (as opposed to that slinger unit), but the casualty rate was still far higher than usual in history. But I liked the length of time it took before the units broke.
Now, if the units are made to break at lower loss percentages, by lowering their morale, for example, then the battles in PB would be over more quickly. So, if the length of the battles is to remain the same with lower loss percentages, then the kill rate must be reduced. And this means the soldiers would have to fight more (longer) before being able to decimate the enemy.
Regarding the idea with new weapons, if we're able to create a new weapon, like a mace of the type which Blemmye warriors used, isn't it possible to assign that weapon to an existing unit (replacing its current weapon)? Creating a new unit for each type of new weapon sounds like more work, which should be avoided, if possibe, in order to speed up dev times.
As for the expanded rosters idea, I need to do some research before being able to suggest changes for all factions that ought to be considered for an upgrade here. All African and Arabian factions are currently limited to about 7-10 types of units (not counting siege units or ships). Other factions have up to four times that number, I think. But we can discuss this in more detail with PMs, yeah.
PS. Is it possible to have the cost of maintaining a unit dependent on the manpower of that unit? Because it looks like the cost remains the same regardless whether the unit is in full strength or down to 1/20 of normal manpower. If so, then it seems odd and perhaps a better idea to disband units short on men and recruit a new unit rather than wait for the weak units to replenish themselves.