I would say you changed the tires at the appropriate time, regardless. My P Zeros were starting to chip into the wear indicators in the grooves at 20k miles. Apparently, the OE P-ZEROS are known for their ridiculously poor treadwear, even on other makes and models.
I currently switched them out for another set of Pirellis, this time to the P7 All Season Plus. Compared to the P-Zeros, these have a much higher rated treadwear and all around performance and comfort as well. Time will tell how long they'll last but I'm hoping the treadwear is just due to those specific tires. Everything else, though, it feels much better driving on these tires. Less noise and better comfort on top of better braking.
I still need to get my rotors resurfaced, though. It wasn't covered under warranty for me either so I'll have to pay out of pocket.
I will say, though, that the brakes shaking only started happening after my car decided to slam on the brakes due to the Emergency Braking System detecting a car slowing to a stop for me to park into a parking space.