In China, if someone is using the luggage compartment above my seat, I just take out their luggage and leave it in the middle of the aisle. I then place my own carry on in the slot above my seat. If you are too far to see someone else take your luggage out, then you’ve placed your luggage too far from your seat. If you see me take your luggage out and you yell at me, then I tell you that you should put your own luggage in the compartment above your own seat. If you have too many carry ons because you also bought a buttload of duty free stuff, that’s your problem, not mine. If you say you can’t put anything in the seat in front of you because you need leg room, then you should have upgraded to a better seat. It’s common practice to just move other people’s stuff out of the way, and it’s up to you to keep an eye on your belongings.
I don’t like having my carry on stowed even if it’s waiting for me by the plane door upon landing because I keep medications, wallet, computer, phone, keys, etc. in there and don’t want it out of my sight. Also, I sometimes need my medications while I’m in flight.