In my vanilla 1.5.8 campaign I've noticed that "participating" in battles is turning nearly all casualties into ***deaths***. This causes Medicine to level extremely slowly because there are few wounded, it also causes many lord deaths if you have that enabled. By contrast, using auto-resolve ("Send troops...") generates more casualties but fewer ***deaths***. This seems to happen across the board regardless of Medicine or Tactics.
As an example with 45 Medicine, 85 Tactics with a battle I tested repeatedly (roughly 100 vs 100):
1. Click "Send troops..." get ~10-15 dead, ~25-40 wounded, 40-50 prisoners.
2. Click "Attack" and hit F6, get ~20-25 dead, < 10 wounded, 20-30 prisoners.
It's a consistent pattern. I get loads of prisoners and Medicine actually levels pretty well when I get 20+ wounded out of every fight using send troops.
As an example with 45 Medicine, 85 Tactics with a battle I tested repeatedly (roughly 100 vs 100):
1. Click "Send troops..." get ~10-15 dead, ~25-40 wounded, 40-50 prisoners.
2. Click "Attack" and hit F6, get ~20-25 dead, < 10 wounded, 20-30 prisoners.
It's a consistent pattern. I get loads of prisoners and Medicine actually levels pretty well when I get 20+ wounded out of every fight using send troops.