I’ve often wondered whether it’s the system getting unfair criticism. Plenty of teams concede loads of goals from set pieces that go man to man, and some of the best Real Madrid, Chelsea etc. teams went zonal and I assume could defend set pieces (maybe that was their weakness, not sure). Maybe a mix of both is sensible. Have your best header of the ball free to attack anything, have a first man doing that space, stick someone penalty spot ish and go big for big everywhere else.
However, I think you’ve got to have the players to do it if you’re zonal marking. Big difference between Ramos, Carvalho, Pepe etc. and our lot of absolute jokers. And maybe the top quality players saved a bad system.
In short, it’s obviously not working for us.