Ever used for example YouTube with an alternative browser?

It's buggy, it's slow (and that's on purpose; Google puts regularly quite some engineering effort into using web features that don't work well in the last independent competing browser). But those Google pages have a big banner saying it will work better in Chrome, and asking the users to "try".

That strategy works very efficiently as Google controls the sites most average people use the whole time.

That's one of the reasons why Google's monopolies need to be broken by regulation. Actually they're over-due for a break-up.