In either case, I feel like this discussion has already been derailed, so I'll just get back to the point.
So long as you're contributing with helping out your team and securing victory, then I don't see why it's a big no-no if someone wants to play with a preferred character or two (hell, even just one). I know the point of the game is to get familiar with the cast and adapt to the playing field whenever it's appropriate, but not everyone can do it. Hell, it wasn't until I reached level 20 that I decided to try to get better with the other heroes, aside from my mains being Lucio, Zarya, Mei, & Pharah.
I agree.
Last night I had someone "We don't need two Pharahs" can someone switch to support...
I was like "Breh, there will be at least two turrets staring you in the face as soon as you round the first corner and that is IF they do not have a Symmetra on top of it...go with the flow"
And I was right, the other team was posted up hard.
There is no magic combination, and having one of each is not a key to success.
Having people play toons who they are good with is far more important than them playing one with a title.