The devs have actually talked in earlier OW2 about how players slept on Sigma. They’re aware he’s good, and they’ve been aware he’s good for yonks. All it really takes is to eyeball the t500 leaderboards in pretty much any given season to know that Sigma’s strong.
But… most people don’t really seem to care, probably because there can be options to deal with Sigma. Winston is a nightmare for the poor guy. All he has is boulder to keep the likes of Rein, Zarya and Ram off him; if they can get in, they can pummel the seven shades of snot out of Sigma. In the DPS roster you have beam characters and flankers who can simply get around him and mulch his backline. Supports have characters that can enable a rush/dive or offer good barrier break themselves.
I say “can be options” because all of that goes out of the window when you see this:
But that’s not Sigma’s fault. Sight lines becoming longer, longer, longer still over the years is a problem going back to post-launch maps since OW1. And Sigma makes tanking in these hellholes more bearable. Who else are you going to pick to stop your team exploding when red team’s Widow comes a-knockin’?