okay, since this isn't a suspect test thread I'm not entirely sure if it's appropriate for me to post this but here are my thoughts on Mega Metagross, mainly coming for a teambuilding perspective :
I'm primarily a bulky offense/balance player, and MMetagross is probably limiting to teambuilding on that particular playstyle than anything bar maybe Mega-Sableye. Since bulkier teams give a bunch of switchin opportunities to MMetagross due to its bulk+typing+speed, you need a pretty consistent answer to it (if you just rely on a Meteor Mash resist like Rotom-W you can't guarantee he'll go for Meteor Mash the second time, or the third, or the fifth, so you want something that can switch on all its moves) and those are actually tricky to fit and not really that great for the most part. Assuming SR are up, they are more-or-less limited to mixed defensive Slowbro, Skarmory (too passive for balance), Roost Scizor, Gliscor, Physically Defensive Mew, Bulky Starmie, Alomomola, Doublade (once again, not good on balance), Gourgeist-XL, Synthesis+EQ Tangrowth, Physically Defensive Arcanine and Delphox (yes, going there) and that's just the STABs/Hammer Arm/GK set alone, the list decreases a bit when you factor in Ice Punch and EQ. Besides Slowbro, none of these are particularly good and most of the time you'd much rather not run one of the Pokemon on this list, so being pretty much forced to run one of these on every non-offense team is really annoying.
Ultimately, my problem with MMetagross is that the switch-in ratios are too much in its favor. We have powerful wallbreakers like MHera and MGardevoir who are almost impossible to switch into, but they can't switch in on too much either. On the other end of the spectrum, we have really bulky Pokemon like Chansey and Skarmory who can switch in on almost anything but deal little to no damage back. Generally speaking, we deal with a certain Pokemon by giving it less or equal opportunities to switch in as we do to switch into it, so none of these are really huge problems to deal with. But when we have a Pokemon like Mega-Metagross who not only switches in easily, but is also hard to switch into, this it forces a ton of pressure on teambuilding since it makes it very difficult to find an equilibrium between it switching in and you switching out, and you end up resorting to full counters like Scizor which makes you weaker to other stuff you'd rather not be weak to in return.
I'm really starting to dislike Mega Metagross's influence on the metagame and the way it twists teambuilding, at this point I'd rather see it suspected than Mega Sableye (not that I don't want to see that centralizing piece of shit suspected too)