TV and movies aren't very immersive - how could they be? You are safely outside the perspective.
When a movie wants to scare you, for example, it tightens up the shot so you're right there, as much as possible.
FPP would not invalidate customization at all, you simply wouldn't be staring at your own ass all the time. You'd have to actually look at yourself. Like in real life. Funny how people dress to impress IRL and don't complain about the lack of a camera to watch themselves.
Take a lot of selfies if you need to.
The FPP fans will absolutely notice a difference if TPP is the default - all TPP-based shooters are clumsy when it comes to first person. All I can think of. Good FP perspective actually requires a bit of work in order not to feel floaty and disconnected. TPP, by nature of you using invisible puppet strings, is disconnected from the get go.
This is a fun argument, but here's a thought:
How will we even know what the "default" for CP2077 is? Heh. Maybe it will be TPP and they screw up on it or you don't like it somehow. Unless CDPR tells us, we will never know what the starting and primary perspective is. Ever. Evvvverrrr.
I hope they don't tell us.