I mean the number of champions is fine. Last I checked currently something like 53 champions in TFT, there was around 60 in Dota Auto Chess. So can use Dota auto chess as a test case for whether the increased 4 will really fuck you over in finding what yo uwant or not and it probably won't. Adding a couple more is fine, especially with the changes to damage as well as streaks meaning people should have more gold and live longer meaning that without adding more champions there would be a naturally bigger chance to find the champions you need. So adding 4 champions might even keep the variance about the same as it is already.

Perhaps controversially, I also believe there should be some inherent dangers to focusing in on a single character to complete your comp. I think flexibility is one of the core aspects of the game and think the ability to find whatever yo uwant whenever you want would make the game more about just min-maxing the best comp everytime rather than figuring out how to work with what you're being offered. But maybe that's just me

As for the idea they should swap out units every season... I mean sure. They probably will do that. It's not the end of the season though so who knows. One of the whole advantages of using skins (i.e. Pirate Graves/TF) to demonstrate origins is that you can add alternative origins to champions so would be alittle weird if they didn't plan on swapping out champions periodically. Rotating them all out is probably a little too much though. Kind of like a TCG you don't usually rotate all the sets out at once but do so a couple sets at a time. That way some existing stuff is leftover as well as space to innovate new comps.