Ooh, hey daddy, come here often?

Moving on to something much better! I'm liking this a lot so far but I feel like I'm missing some battle mechanics. For instance, one character is weak to electricity and was just getting their ass handed to them in a boss fight. So I equipped this character with an item that boosts elec defense, and used an ability to raise defense against electric attacks in battle. The character was taking easily four times as much damage every attack. Way more than the 50% more damage he should be taking from his vulnerability alone. But this is also with those two boosts! I don't get it.

I also haven't quite figured out Isaac yet. What's the point of his different forms if everyone generally takes a quarter to a third of their HP per every enemy hit? Shouldn't he just always be tanking? All of which makes battles feel monotonous.

Point in their favor, I'm about 9 hours in and I already cried, lol that might be a record.