I've recently seen FA's pulling a few personal items from the OH's to make room for full-size carry-ons and when there has been a fuss from the passenger, offering to gate check.

There is no "right" to OH space even if one only has one carry-on and it is of the "personal" size.

Needless to say, this only works when the aircraft is boarded fairly early as it takes time.

But, it's a zero-sum game. Some winners & some losers.