I wrote about this topic earlier, I believe there is one main reason for Apple to go in this direction: universal design language (spatial computing, Vision Pro). Of course, there can be many side-effects (or reasons) that can be the actual main reason instead, such as 'innovation' or like you mention, guiding people to use the native systems, we'll never know. In my eyes, the universal design language is the main reason. Apple is and always has been design-focused.
Yes, I've been on all the public beta's so far and yes, you can turn it down. You can turn on 'reduce transparency' in the accessibility settings. It breaks most of the effects, but text is definitely more legible. Haven't noticed anything performance wise (when Liquid Glass is turned on), but then again I might not be the best test candidate as I just got a new phone.
I stumbled upon a lecture by Josh Tenenbaum (MIT) yesterday. Starting from minute 19 he talks about world models, and how we're nowhere near 'real AI'. This lecture was from 7 years ago, I wonder what a more recent take from him on this topic would be. https://youtu.be/TFyAEHk5asY?si=lZfjeF7t66FhkdSZ&t=1157
