I agree.
It’s great they buffed Sombra as a counter to mobility, but Sombra is a flanker as well thanks to her better mobility. She will not protect teammates because she is too busy being a flanker and disruptor.
Defense heroes who lack any mobility should be the one who protect teammates. Heroes like Torbjorn, Bastion and Mei of course.
Geoff himself said that Mei’s role is to slow down enemies, but her problem is that she can only slow down horizontal base movements. Vertical movements and mobility abilities are ignored.
Mei is not the answer to deal with flankers and mobility.