I have already turned my back to the game, but gave it a try in 1.58 the other day. Ouite shure the devs changed something as I had the same battle experiences as you have had. What looks like an easy sweep turns in a slaughter with appalling losses once the battle is over. Often enough my forces were utterly crushed and I found myself in chaines...
Let´s look where it might come from. I noticed that the AI Armys have a much better line up then some month ago. No more recruits and tier 1 troops in abundance but a good solid army composition of experienced troops with a lot more cavalry as we has been seen previously. I noticed that the enemies heavy cavalry spawns when the first wave of the enemy is broken and our troops are in full pursuit. Thus before I am able to comand, control and regroup, the entire engagement is going worse turning to a bloodbath.
I noticed also that only the first rank of my archers is firing, second and third rank fills in the losses only. Not like the enemy, which is aproaching in skirmish order with all men firing. Once given command to the sergeants, my archers run to and fro and are even less useful, being cut down by enemy cavalry in the end.
My heavy cavalry is getting spiked up by enemy spearmen as I have no control which enemy they attack unless I lead them in person.
It seems that engaging the enemy in batlle has become as much frustrating as every thing else in this game. Well the game, it looks good, at least...