At least Sombra doesn't nearly have as much mobility or durability compared to Ana and/or Mei, and she only has one, very subpar attack and one mobility option that's more campable than Reaper's.
Mei is agreed by virtually everyone with any skill to be pretty bad actually, she's basically extinct at even mid level public competitive, most of the defense heroes are bad actually with only the snipers being exceptions if the guy using them is notably above average.
I was watching the Overwatch championship stuff on twitch. I didn't watch every match, but all the ones I did watch had Mei on one of the teams. No one was talking about Mei being bad, at all.
Mei is agreed by virtually everyone with any skill to be pretty bad actually, she's basically extinct at even mid level public competitive, most of the defense heroes are bad actually with only the snipers being exceptions if the guy using them is notably above average.
You're way behind the times, man. Mei has been both good and highly used in Pro games for months.