I have a Kindle and I have a Kobo. It is true that I have more font control on the Kobo than I do on the Kindle, although on side-loaded books much of that control doesn't seem to work. I have read in this forum about ways to deal with that and I tried a few and they seemed to work okay most of the time but they're really just not worth the trouble.
On both devices when I'm picking a font size I never really find exactly what I want. This can be irritating when I'm picking the font size. I've learned, however, that whichever size I pick seems fine when I'm reading. It's only when picking font sizes that it bothers me.
Barry