So basically it is to have shorter battery life despite advances in battery technology, and have planned obsolescence? This makes this even more compelling to leave their ecosystem.

This is just jumping the shark, as they need to push out something that can be talked about their products, and Apple Intelligence is a flop so far. As the saying goes: “There’s no such thing as bad publicity.”

I have an iphone 11 (non pro) I use as a GPS. The update works fine on it, I haven't noticed any unusual slowdown. If I'm not mistaken, that's a 6 year-old model, and I think it's the oldest one supported.

I can't comment on the battery life, since it's plugged in almost all the time. I haven't noticed any change on my regular phone (14 pro).