@Wainan It is a fascination of mine to watch games and how different people react to his strategy so I have seen a number of different approaches.
I've seen people try MML spam, but by the time they realise that they are facing a determined turtle, he is usually up to T2 build power already and can build T2 static arty which renders MMLs a complete waste of resources as it loses hard to artillery+shield.
I faced him once more since starting the thread, on Vulcan's Reach. Due to my clumsiness, I allowed him to get established in the upper right corner of the map, but otherwise I took complete map control essentially unchallenged and instead of trying to invest any serious effort into breaking down his front door, I kept him occupied with some small T1 land armies as "bait" for his radar (he rarely ever scouts anything at all, least of which your main base), as well as some "annoying" with UEF Sparkies while I spent all my mass on upgrading to T2 mex, ringing them and starting T3 mex upgrades; while investing the rest into power, engineers and a T3 air factory to just put an end to the grindy game with 11-12 Ambassadors to his ACU. This takes time however, and is not really what I'd call an entertaining way to play the game.
He played as he does every single game. Starting out with expanding, totally unprotected engineers out of his first factory, and if they reach their intended expansions, he builds a single T1 PD and T1 AA before factory making it extremely open for a swift denial if you just pay attention with your early raiding units. If you fail to take it down early, he will build Lobos (practically never tanks) for scout-less harassment and defence, until he can fill that base with T2 PD, and T2 artillery if you try to kill the base. His end game is practically always shield SACUs point defence creeping across the map and a Novax followed by a Duke. My strat snipe came shortly after he plowed all his resources into the Novax.