I think the issue with what you're saying is you're applying a long term mindset to a short term mon. If darkrai is going to be consistently allowing in strong breakers such as iron valiant, mega lopunny or urshifu to gain momentum every time it clicks dark pulse (although i am aware it also has coverage for these), then it won't be able to come in 4 or 5 times to be able to kill these checks over time. It's relatively vulnerable to being chipped down by hazards and it's weak to u-turn allowing it to be freely pivoted on without worrying about them staying in and claiming another kill. The offensive teams that it thrives on can't afford to let in strong breakers every time it clicks a move because they don't have the strong defensive profiles of fat or balance. It's essentially like saying that tapu lele is broken because heatran can't switchin to specs tera psychic more than 2-3 times - which in practice is true but in reality every time that heatran comes in it gets rocks, a toxic or a potential trap/huge chip with magma storm, often gaining massive progress. Of course sure if we just look at it in a vacuum heatran can't switchin more than 2-3 times, bulky mega scizor is 2hkod and most dark types are frail or prone to hazard chip, not to mention that they're nailed by moonblast, but in an actual game it doesn't function that way - and I think that's what people are getting wrong with darkrai.
It's obviously on another level to something like hoopa-u or ursaluna just due to it's speed tier, good defenses and great coverage, but if we use the same mentality and put those pokemon in a vacuum of only the turn where they're attacking - then they're broken as well. Before you haha react me into the ground i'm not saying to ban ursaluna or hoopa and i'm not comparing them to darkrai in power, i'm just showing the flaw of the mentality that many pro darkrai banners use. There IS counterplay to darkrai, just not in the form of some blanket check that beats every single set, which is fine. Most people are going to be running darkium z for example, so something like ting lu, mega tyranitar, spdef clefable, clodsire or defensive kommo o are fine as checks and all of these are able to get value out of darkrai in some way such as getting up hazards, clicking status, or setting up. Once darkrai uses it's z move it becomes significantly less threatening and it's usually not difficult to land a toxic on it with a toxapex or gliscor and at that point it's on a timer, not to mention that many offensive and defensive mons can tera to beat it from almost any position.
That being said, I still understand that it's not on the chopping block for no reason - it is extremely powerful and can be overbearing if you don't know how to play around it - but I think it's wrong to say that it has 0 checks at all, especially because many people assume that it has every set at once when listing out it's checks (for example if its against iron valiant it beats it because of scarf, if it's against ting lu it beats it because of z fighting etc, despite saying that you should always run darkium). For example it's never going to be getting a nasty plot off while there's an urshifu on the opposing team that is immediately coming out every time darkrai comes in, and every time that urshifu comes out it's freely able to click u turn on darkrai as it's weak to it. Even if it lives and stays in it's now on a significant timer as it's weak to hazards due to being low on health meaning that urshifu can now outlast it, not to mention that with every u turn the urshifu is going to be bringing out some big breaker like ursaluna or yard to claim a kill.
I'm personally neither pro ban or against the ban. I think the meta will be able to deal with darkrai if it stays through the rise of pokemon such as chesnaught, kommo o, ting lu, scarf fini and spdef clefable - but I also think that it would take a big burden off of the meta if it's gone.
which is why i made an entire section on how its changed the meta to inhabit a faster playstyle(offense)
this is basically what makes bulkier builds so bad, they cant play the long game with breakers like darkrai bc everytime it comes it something just dies, this basically opens the stage for offense, a very fast momentum heavy archetype, to be so prevalent, not letting darkrai have switch ins and not having games be over 30-40 turns. which is why a lot of people agree on its ban as a stepping stone to let other playstyles be more viable
its not that im using the fact that darkrai has so many sets that can beat its checks to why its getting banned, its moreso adding onto how problematic darkrai can be due to
not knowing what it could click, a scarfed darkrai clicking sludge on koko could flip the entire game state.
yes, with something like ursaluna you can intimidate with rocky helm lando and then pivot to smth like ferro and basically subject it to having to make reads in order to not get chipped majorly, however darkrai rarely has this issue, the counterplay is trying to get ur speed control in to force it out, which oftentimes is really difficult, as it has the coverage to beat mtar and ting lu, and fairies like clef as well, it has that speed tier to be able to basically click whatever
mtar gets focus blasted, and even at +0 its ohko after rocks iirc
ting lu cant really do anything back due to darkrai’s good bulk, you just force it out while taking a ton from focus blast(headcalc 70?)
spdef clef is noticably worse than pdef, since its fairy typing is much more preferred for a physical blanket wall for mlop shifu tusk etc
the inability to use that fairy typing to check mlop effectively is generally pretty sad
clodsire is… pretty bad! it really only fits on stall
kommo i will admit isnt even bad, but its rise in defensive usage by a lot of players is bc of powerhouses like rai and pon, and its not easily slottable
basically just a niche defensive option that rised solely bc of darkrai and friends
also, darkrai could just hard dark pulse into that urshifu and force it to tank that alongside rocks/spikes and chip from partners(which should be alongside it). your argument here is a game state
outside of a vacuum but outside of a vacuum(ive already mentioned this in the original post) it has other duties on a team besides just being a darkrai check, which oftentimes results in decent chip aside from rai that doesnt allow it to be a rai check efficiently(again, the best cplay to this is to not let darkrai in… back to the spam offense circle thats making the tier bad).
also, you have to be trolling by mentioning fini and chesnaught there