Of course it should be the case. It's kind of the whole point. Have you played the game? Some characters counter the other.
If you're playing against a really good Phara for example. You have a decent team setup, but nothing to counter it. You're asking your DPS guys (Mei and Reaper for example) can someone change to Soldier or McCree, but they ignore you all game long and Phara pretty much single handed wins the game. I wont lie, I would be a little annoyed with them both.
They could be amazing Mie's and Reapers, but they simply can't deal with a decent Phara.
Personally, I wouldn't report them, I would calmly point out they've not helped the team and contributed heavily to the loss, due to their reluctance to change, but if everyone else reported them for not playing as a team, I couldn't blame them. If they can't play Soldier or McCree, offer to switch to support or tank so someone else can. If they can't play any other characters, they probably shouldn't be in Comp tbh.