Vitinha only missed 3 games due to resting in that season and was injured for 2 games. Enrique rotates a lot cause he has quality depth with the likes of Kang In Lee (who's now leaving), Zaire Emery, Ruiz, Joao Neves. It would have its merit, but you need quality squad depth to implement that, and you'll still see some players getting annoyed with not having enough minutes
Now we were leading Madrid by 6 points before playing Espanyol, and Espanyol had lost 2 times in their last 3 games while drawing 1. In fact, they haven't won in their last 11 games and more, and we were winning 2-0 by 25 minutes; why didn't we rest our players? An Enrique now would've rotated since that's what he does to avoid injuries while still keeping the squad happy.
That's why I think it's an easy excuse to say we lost in UCL to Athletico cause Pedri was tired and Leggy, and Yamal got tired at the end of the game, cause we had opportunity to rest them and didn't, and that's on us. Funny thing is you could rest the players, and we also lose (some people then would say the players are lacking sharpness).
Don't forget that Arsenal won the same Athletico despite still being in a tighter battle for the league against City, infact they played City, then Newcastle and Athleti