The reason battles are so fast is because IA fully commit to attack, both sides clash with full force and within minutes one side gets wiped out entirely, while the other loses half of the manpower. I've even seen an instance of Surgia vs Vlandia battle, where Surgians had significant advantege but lost miserably because of the stupidity of such tactic. They attacked defending vladians at spawn point, where Sturgian infantry got sandwitched by the respawning vandian force and a unit of crossbowmen.In the meantime sturgian bowmen got massacred by vlandian cav. And ongoing Sturgian reinforcements made an easy pick for both xbows and cav.
While battle tactics are way improved over Wrband, the situation described above still doesn't make any sense from tactical point of view. Real battle should open with skirmishes. Archers and light cav should be sent in advance, trying to open the enemy formation/weaken the force/ provoke attack etc. Light cav should go aganst light cav, winnig cav should charge enemy archers. Only after one side manages to route the enemy skirmishers, they should commit full-force to attack weakened enemy.
When I play I always try to use my cav as skirmishing force, luring enemies into ambushes etc before charging in. Battles payed this way can ctually last quite long and be somewhat interesting. But this is only possible when players army has an advantage, otherwise enemy just charges their army mindlessly anyways.