The Exynos variants of Samsung devices can have their bootloader unlocked, it’s the snapdragon ones that can’t and even then there are some instances where it was possible to do it, but it’s still a hassle and the Exynos variants tend not to have good development support.
Not the same person but I’m using Nova on my pixel, for starters icon pack support is a must to me, and then Nova lets me tweak things on a granular level, so I end up with much cleaner looking launcher, no search bar, no scrolling bar, customizable background color, text color etc and that’s just a few advantages it offers.