I did this because I disliked the interface as well. It worked fine for me.
However, I am discovering that Amazon has sneakily put enough safeguards to prevent users from changing launcher. The search feature of Fire stick is tied to its launcher. If you disable the inbuilt launcher, you can no longer use the search feature, not even in app store, since it relies on homescreen search.
Similarly, interactions with Echo devices also rely on the launcher. So you lose the ability to play videos directly with Echo, though, you can still launch apps.
In essence, Amazon has done enough to force our hands and make us stay with the default launcher, which basically converts your screen into a gigantic ad screen. I'll be going to the default launcher and will try to figure out a way to launch Kodi automatically on start.