The greasy key effect on the new gen keyboards does bug me a bit (just because some keys show it more than others due to use), but not enough to use an external keyboard just for that reason. When my MacBook Pro is docked I'll use an external keyboard, but when it is not docked, I don't have any problem using the built in keyboard on my MBP.
That’s all I do. It’s a reality, if I’m not getting grease spots (and I have clean hands), then I just not be using it enough. Lol.I didn't get my first Mac until 2014, but by 2017 my 2014 MBA had greasy keys all around. TBH I think this is inevitable and not worth losing sleep over. I'll rub the keyboard with a (lightly) wet microfiber cloth every once in a while and that's it.