5 dps teams basically never happened, at least at my rank. And the few times it did it didn't always end up in a loss.
And I definitely remember the shitty parts and there were fewer of them. Imposing a restriction does just that, restricts flexibility.
Part of the blame falls on everyone, but when you're Zenyatta and you have most elims and most damage, unless I'm having an amazing game the DPS are not pulling their weight, and being unable to swap basically means losing a game.
I remember winning games by just changing roles within the team, can't do that anymore. As an example, If our best pharah is locked playing tank, then we can't run pharah+mercy on a map/vs a comp where it would work.