ML is not for map control, because it's a weak unit for it's mass (even in 3599), located in one point. Actually MLs cost was raised to be 17k specifically to balance it so that it wouldn't be rush-effective. Don't forget, that travel time for ML is going to be no less, than 2 minutes, it was enough to build a GC when rushing GC symmetrically even in 3599.
T3 bots are much better in map control (well, pretty much anything, including T1 spam), and in killing bases too.
Also in ML-rush scenarious, some players are so affraid of, the rusher will have much worse economy (we suppose players are of the same playlevel). In basic RTS mass-power concepts (not to be confused with mass-energy, mass here is units, power is economy), T4s are concentrated mass, and this also makes a player to commit and wait, and gamble and probably lose because of this. For me, T4s
should be better than anything else for their costs. Now we consider, should ML be 1/2 mass-effective (9 or so percies kill it), or a bit better, like 2/3 mass-effective. A shame
Also even on very average playlevel, everyone adds T2 flaks to T4 as otherwise T4s are destoryed with <10 T2 gunships (3,2k mass) half-way.
I seriosly suspect, that all this whining about T4s being OPed is caused by players who are being constatnly outplayed and locked in the base firsly and roflstomped with T4 consequently for lulz. I, personally like to do it alot. Probably I shouldn't as now they nerfed ML... But I guess, I would do it anyway.
Care to watch replays, guys, don't blame some expensive as life unit in you failure, blame yourselves.
Best wishes