I would understand if Atletico let go of Simeone for a tactical shake up alone. But my issue is less tactically more about morale. Having to deal with Messi and Ronaldo every year for close to a decade across all 3 non-Europa league competitions has to take a heavy toll on the motivation of the squad. Both facing them directly or just trying to keep up with them in the league. I'm not sure any manager in the world could have motivated them regardless of tactics. Which to me, seems a little unfair on Simeone.
That's not an excuse to only score 39 goals with ten games left in the season. They have the best defensive record in the league by a mile, but at the same time, they've scored one goal more than the 15th placed Levante. You can't use Messi and Ronaldo as an excuse for that. He's not managing a bunch of mid-table players either.
Again I understand the losses against Real and Barca in knock out competition, but you can't use that excuse when you're playing defensive football against the bottom place sides in the league. That alone is a tactical issue not a morale issue.
And if you cant motivate the players any longer then you have to step aside for someone who can.