Re Messi's (and Ronaldo's, too) decline, this is something undeniable. Even in the game vs Juve, he lost the ball several times that made me think that "in his best years, no way he loses the ball there." He is still great though, and is still the difference maker. Neymar, for all the praise he gets, wasn't able to outshine the current Messi. Though he lost some pace, acceleration, agility etc., he is still more reliable than most in tight spaces. He does the basics right, he is best at the basics.
Suarez is the one that has been surprisingly poor so far. No control, no dribbling, just nothing is going for him.