For one, USA isn't actually much better than China when it comes to tracking and privacy. They just have better PR about it. But in reality they equally suck.
That asside. There isn't some secret tracking chip, but any kind of wireless network will be used to track you by different parties. Cellulair, Wi-Fi (including Wi-Fi signaling when it's "off"), Bluetooth, etc. This is a fact regardless of OS or where the phone is made, as tracking often already starts to occur by catching the signals you send out.
As such, just degoogling won't resolve tracking issues in and off itself, it's just one of many steps to get less tracking.
Phones physically in China, regardless off where it's made, tend to get tracking software installed. Just take a burner if you ever go there. But that's not hardware. And most "USA" phones are also made in China anyways...
Average Joe wants an easy all-in-one solution. That's what Google, Apple and Microsoft offer. An ecosystem. If you want to fight that, you need to be able to offer that. So that's what Proton is doing.
Of course it's better to have it seperated. And the security and privacy nerds will likely keep doing that anyways. But Average Joe doesn't want to take a hassle and rather looses privacy than do that.
Issue is, things are only as secure as the least secure point. Average Joe using Google and Microsoft means your data also goes there when interacting. When Average Joe is swayed by a place that is privacy-friendly ánd convinient, it makes your weakest link also stronger.
Meanwhile, Average Joe is also more save then when he was using Google or Microsoft services. Even when he would be less save than if he had his stuff seperated.
It helps everyone.
With that in mind, I applaud it. But I won't use it. I use Proton for mail, Joplin for notes (encrypting them in Joplin and syncing with NextCloud), and my passwords are also elsewhere than ProtonPass.