Apple does not allow carriers to modify the OS. Google could demand that they leave Android alone also if they wanted to. They've pushed a lot of functionality to google play services to get control. They could push that all the way.
If you look at the update builds for Pixel phones on the Google developer page, the pre-Tensor phones have very few carrier specific builds. The vast majority are just a single build for the update. If you look at the Tensor based updates, there are fragmented builds all through the various 6 and 7 phones. Sometimes it is Verizon with a special build, sometimes AT&T, sometimes others.
Something about the Tensor allowed (necessitated?) this. That is on Google as it is "their" chipset. If I were guessing it is the non-qualcomm modems meaning the carriers have to tweak things. And once they get a toe in, they seem to be doing other things.
While I appreciate that the customer experience is different for everyone and understand how frustrating things can be when they seem beyond our control, I personally consider my Pixel 6 Pro to be one of the best devices I have ever owned. It came with a stock Android OS, it's fast, consistently reliable (so far), takes some pretty good pictures, and has a decent battery life - all at a decent price.
Perhaps I am dealing with an anomaly, but irrespective of chipset, my carrier has not touched/tweaked the stock Android that came with my Pixel 6 Pro, nor have they tried to add anything to increase their footprint/control on my device. Why would Verizon feel a need to do so and why would consumers continue to support a carrier that would manipulate the core functionality of their (unlocked) devices?
While Apple might be lauded (or denounced depending on the things you value) for locking up iOS tighter than Fort Knox and for making things simple for consumers, I personally prefer the greater choice that the Android OS brings to the table. Things like deep customization and personalization options, a universal file system that I can actually see, use and drag and drop onto my PC, the adoption of a universal (as opposed to proprietary) port system, brisk continual innovation, etc.
It wasn't my cup of tea, but it is for a great many consumers. If you end up moving to an iPhone, I hope that it provides you with the things you are looking for in a device and provides you with a great experience.