Hi, everyone.
I have very little to add, since Dracolosse has summed it all up.
First of all, the fact that you need to think through and choose wisely when to dmax is pretty huge for me. It is honestly a really good argument pro-dmax. That is not uncompetitive or braindead at all. It is another layer of skill one has to account for.
Also, yes, Dmax is a gen defining mechanic and I don't think that has been taking into account properly. If we ban, we will have 3 or 4 years of a meta with only mons? No megas, no Zs, no nothing? Gyara, Togekiss and some other mons like ditto will get a little worse and that is it - an entire gen defining mechanic in exchange for a few mons becoming a little worse.
Not only that, but Dmaxing basically is as if every single pokémon on your team could mega at any time, with the restriction of 3 turns of dmax. Megas boost stats, make bad pokemon like lopunny and Kangashkhan rise from NU to OU or ubers. And, as someone mentioned before, there has never been a debate of banning megas altogether. So what if Dmax makes some pokémon better, like Hawlucha (which was already a pretty good late game sweeper in USUM and has been proven to be an ok mon, not broken at all), Gyara (again, another pretty good mon in USUM, with Z-Fly allowing it to beat many counters), Togekiss and so on? The same could be said for megas and for z-moves (Z-Fly was huge back in the beggining of S/M, with salamence, lando, gyara and dnite).
Truth is dmax is pretty much a mega for any pokémon, aside from the no item restriction (actually, you lose the choice item bonus, which is also something that one needs to account for in game). Yes, it makes them bulkier, but only for 3 turns. Yes, some moves have pretty nasty effects, but, again, they can be used only for 3 turns, you actually lose access to status moves while dmaxing, and it is not like mons are unbeatable while dmaxing. There are so many ways to play around, one just have to think outside the box. I mean, how many teams have I seen running counter or metal burst in these past weeks? None, aside from my own teams. Only dittos and maybe a prankster twave once or twice, or a mimikyu. And if the opponent can abuse fly/fight dmax, so can you. If the opponent can dmax to withstand a hit, so can you. Unless, of course, you build your team poorly and don't account for that specific mon, or if you play poorly and sac your check early game. Or it could be that the opponent cteams you, which has always been a possibility.
In short, there is no argument against dmax that can't be properly answered by the fact that you can also use dmax in your favor, at any time you want (to grab momentum, to try to remove a particularly annoying threat etc.). Or, in other words, I feel people are just being lazy throwing dittos everywhere and complaining about dmax. I mean, Trick Room is crazy good in this meta, with great mons to abuse it (perrserker, copperajah, pinkurchin, hatterene etc.), but I rarely ever see TR (aside from hatterene, these other mons are all UU rn).
Gyara is everywhere? Well, so was lando in every gen, to the point that other landos had to run HP ice, mews had to run ice beam... But we never thought of banning lando. The same can be said for gyara (which is checked, among others, by any scarfed electric type), Darm and Hawlucha (which is honestly not even that good). All you need is a little more time, like months, for the metagame to adapt.
Someone mentioned above s/he couldn't see how would anyone build a team not around dmaxing. Well, in ORAS and USUM, pretty much every team would have a mega. And, in the case of USUM, a z-move. How is that much different? Z-moves made the game pretty unpredictable as well. Is the opponent running z-grass kartana, Z-steelium, Z-normal, z-Fight? Or is the Z-stone with Tapu Bulu? Who knows, thats something you have to account for when teambuilding and when playing v. the opponent.
And the fact that both players have dmax and both players can choose when to use it in order to win a game... I really can't see how anyone would think that is uncompetitive. For me, that is check and mate.
I saw someone saying Dmax makes the game more random. How is that so? What is random about dmax? Dmaxing is the opposite of random.
All in all, dmax has nothing intrinsically new, aside from some immunities, which, yes, is stupid. I will agree the fact that dmax mons are immune to phaze, flinch, dbond and weight moves is pretty dumb. That is the only broken point I see in Dmax, and it restricts many answers to that. While that is true, for me, it is not enough to take down this gen defining mechanic.
In that sense, I believe we should not ban dmax, and that we should have dmax for at least three or four months before we consider banning the whole mechanic.
TL;DR: both players can use dmax any time they want, so they need to think carefully when teambuilding and when to use dmax. That isn't broken, uncompetitive, random nor braindead. Dmax is a gen defining mechaninc, which should be approached as such, and it doesn't bring anythin intrinsically new to the table, aside from a few immunities (dbond, flinch..., which I don't think is enough reason to ban it).
