Thanks for catching a couple of typographical errors. I've requested edits regarding the companies. I'm well aware GMK and SP are different companies and ePBT and EnjoyPBT are the same. I own sets by all three
I think we're getting into the weeds elsewhere, though. ABS vs PBT longevity is related to shine. In terms of wearing out completely, who knows, but one will look worn before the other while potentially costing significantly more.
Likewise, sound profile is going to vary. However, PBT is a denser plastic and that will impact sound all by itself. The question is by how much. I tested multiple sets on the same board and can clearly hear a difference. That said, I didn't have calipers on hand. Perhaps the caps are 0.1 mm different (visually, on close comparison, they look the same).
For the feel of thicker keycaps, I stand by my experience. To me, thicker keycaps have always felt more solid under the finger and I know that is echoed by many. You're right that other elements impact that, though. But, tested on the exact same keyboard, thicker keycaps feel more solid and that makes sense when you consider the increased material impact vibrations need to travel through.
As far as case plastic, sure, there is more than ABS out there. But, there's a lot of ABS. Shine is a result of repeated wear and you do see those cases shine over time, usually where the wrist or palm touches.
Thanks for taking the time to read and comment. One of the things I love about this hobby is how nuanced it is!