Basics units even when capped at 20hp/sec do not regen hp. in fight or outside fight, sometimes work 80% of time not work.
overheal make units have 9k health in open world menu of army, they appear "wounded" with 5-9k health if you go in a city and try to heal them, it cost 10k gold.
if you go in fight they have full hp with normal values. but this make impossible understand how much hp they have in open world. since it says 4500/9000, when in truth they are full at 2000/2000
you can train all units up to lev 10 except for dwarf shooters. and they are extremely slow to level (all dwarf units ) i can literally bring a human units to lev 20 faster than i get a dwarf unit to lev 12-13
also upgrade like : more weapons dmg for your knights etc, seams to not work, i mean you develop it, but knights dmg remain 103 even after the upgrade, same for piercing crush slash resistance, more healt points : there is no visible benefits from upgrades , you research the upgrade but on the units stats there is no change at all