Well, Apple is giving me more and more reasons to switch away from their default apps (which I used to love) with every release. They focus too much on new features, too little on stability and good experience.
I've already ditched Music (macOS: Cog; iOS: Decoupled), I'm holding off upgrading for Photos' sake, Home on macOS is an absolute nightmare, Mail is meh but ok (fingers crossed they won't accidentally break it), and I'm hoping they will never go after Notes - it's central to so many things in my life.
Meanwhile, I'm still using Emacs, because despite its many shortcomings (mostly the legacy architecture), ELisp makes writing simple plugins simple, and the few that I use are too excellent to get me to switch.
Without it, you have to use so much glue for a good experience. So, look at the very popular extensions and see if they can become native.