It's not up to the "core devs". It's up to the big miners. They control block size.
Nope it's not only up to big miners. It's also up to every full validating nodes. That's why it's a hardfork.
Who is going to want to fiddle with fees after they send a transaction? That's like the postal service getting bogged down around Christmas and letting people know that they can send in extra postage if they want their packages by Christmas. It would be a hassle and universally annoy people.
You only need to fiddle with fee if you are greedy by taking the risk to pay the very least fee.
The dynamic blocksize increase only makes sense if you can securely project the rate of increase in block size needed. If you guess wrong then the trajectory is off and you end up needing to hardfork again anyway at some point.
No, you didn't get the point. The goal is not to project anything. it's to make sure Bitcoin doesn't become centralized and it's to incentive offchain solutions. if you don't care about decentralization, why don't you just use ripple? Ripple scales great. Lol.