For Maxi you forgot, a guy of his size is going to struggle with the physicality of the MLS.
I don't equate "physicality" with just strength. Physical skill is definitely required in MLS, partially because the technical skill level is low, so the players have to differentiate themselves somehow. But physical skill can be size, strength, speed, or quickness. There are plenty of fast players in this league that do very well despite not being physically strong.
I'm not that worried about Maxi - there's no league in the world where he isn't the smallest player on the pitch, so this is nothing new. His quickness, positioning, and skill should disorient MLS defenders.