I totally understand this situation. I actually never had a good mobile set up when I was on iOS and only when switching to Android was able to finally setup something I liked using orgzly-revived, syncthing, and android Emacs.
As for GTD, I never did proper GTD until about a year ago, after reading the GTD book. I don't consider my life complex by any means, but I've been surprised at the amount of projects in my life that have been reified in my system.