In my experience it goes more like "I've noticed that when I lose when I often have that character on my team, so that character must be the problem."
This is especially the case with bastion - if someone on your team is bastion on offense, you have to change the dynamic of your entire team to revolve around him. IE, Reinhardt has to shield him, mercy has to boost/heal him, everybody else has to help get him into position and stop him from being flanked, and then he can lock down wherever he is. But a lot of people, myself included, aren't willing to cater to the gaming preferences of somebody who, without prior discussion, decides to make a match all about himself. So we don't go all-in on the bastion offense strat and bastion ends up useless and the game is a de facto 6 on 5, so we lose.
Also, the problem with a lot of offense Hanzos/Widowmakers is that often the players playing them aren't good enough to pull it off