Agreed... but what I think people are really saying is that when both players are equally skilled, the game has a much better flow to it. When one player is significantly weaker than the other, the game plays much more differently. You're either trying to win the game by constantly attacking the weaker player, or trying to be "social" and avoiding hurting them. When one player is much weaker than the other, they are going to be the weaker player from start to finish. It's not totally the same thing as playing I-formation or poaching occasionally.
For example: In Mixed, when the guy is serving a second serve, im going to challenge the girl at net as often as I can and i'm never going to lob. I can do an easy roller DTL to make her reach, go hard straight at her, or just a standard hard DTM return. When the woman is serving, im almost never going to challenge the man at net and I am going to make him struggle trying to intercept the ball. I LOVE to lob returns in mixed when the woman is serving, especially when it's over the backhand OH of the man and will make the woman have to run. This gives me an easy time closing into the net. In mens league, im probably going to challenge each man somewhat equally, but most of my returns will be CC with the occasional DTL to keep them honest.