I personally beg to disagree, Dracovish is a powerful wallbreaker but one that has quite a lot of counterplay which you are not acknowledging, many more exploitable weaknesses and counters than just a water absorber and a large amount of high tier, common, checks.
The first thing we need to note this generation is that rain has not been that powerful, therefore at higher levels of play (which is where games should be balanced in my opinion) more often than not, Dracovish is doing about 40-50% to Toxapex with fishious rend while choice banded, which is still a lot except Toxapex recovers with regenerator when it swaps out, and it has recover, and has baneful bunker to poison Dracovish, there are other answers to Dracovish asides water absorbers at the higher levels of play and while they may not be as good as an immunity, they can do the job well, therefore you do not need to run a water immunity to have a defensive check to Dracovish but it is nice to have one.
The next point I would like to address is water absorbers, specifically Seismitoad, a common misconception is that Seismitoad is only good because it is a defensive answer to Dracovish, but that is far from the truth. The reasons Seismitoad is good this gen are mainly 1) it has access to stealth rock and the now uncommon toxic, 2) it has an electric immunity and fire resistance, both of which are key to dealing with Rotom-H, an incredibly popular and powerful Pokemon in this metagame, and by forcing out Rotom-H with its water stabs—which the flying oven definitely does not want to take without compensation—it can reliably set up stealth rock which can be key for getting the chip damage required to muscle through some very bulky teams which are quite common in the Sword and Shield OU metagame as of now. Therefore, even though having water absorb is nice for Seismitoad, Dracovish is not the sole reason it has had high pick rates in the metagame as of late, therefore I do not believe your implied assumption of Seismitoad being only good because of Dracovish is correct due to the numerous other roles it fills within the metagame being more vital.
Lastly, I would like to discuss the multiple options for counterplay to Dracovish and it's many checks by high tier pokemon, such as the everpresent Dragapult, to illustrate that even without a water absorber, there is still counterplay to Dracovish. The first method of counterplay against Dracovish is to not let it have an opportunity to get in a position to do damage. Fairy and dragon type attacks are incredibly common and as such, it is often difficult for Dracovish to find an opportunity to enter safely without taking massive amounts of damage without sacrificing a Pokemon to enter, a reliable form of entry sure but not a very good one, on predicted swaps or resisted moves Dracovish can come in but then that is them outplaying you and as such, if that leads to you losing the match then that was because you were outplayed by your opponent and not because it is overpowered. The next point of counterplay I would like to address is the fact that, because it is so slow, it can easily be outsped by very common Pokemon such as Dragapult of Hydregion and forced into a team member who can tank the incoming attack, a swap which is incredibly predictable and easy to capitalize on from the end of the Dragapult/Hydregion user, and if Dracovish tries to alleviate this issue through the use of choice scarf then it still gets outsped by Dragapult and loses out on the key damage thresholds that make it so powerful, rendering it suboptimal compared to other picks for wall breakers. And the final method of counterplay I will mention is to either burn or paralyze Dracovish, the former from will-o-wisp or scald burns (possibly from Seismitoad) and the latter from the incredibly common usage of thunder wave. When Dracovish is afflicted with either of these two status ailments, it loses a large amount of it's ability to wall break and destroy teams because it is either too slow to outspeed its targets (such as Clefable) and get's OHKO'd by moonblast, or the attack drop reduces it's damage to the point where it hits about as hard as a pool noodle. Either way, Dracovish does not want to get statused. Overall there are more methods of counterplay to Dracovish than just a water absorber such as Seismitoad who, granted, gives an incredibly powerful form of countering Dracovish but is viable because of other reasons and even then, Dracovish can still beat Seismitoad with proper predictions. If your opponent chips down Seismitoad and predicts your swap in, choosing instead to use choice band boosted psychic fangs to do 40% to Seiesmitoad and KO'ing it, then that was them outplaying you and they deserve that kill. If your only option is to use a water absorber to beat Dracovish and swap it in every time it comes out then you are giving them the opportunity to destroy your best answer easily, but because the multiple ways of countering Dracovish, through the use of status ailments, fast revenge killers or just not giving it the opportunity to swap into one of your pokemon it wants to take out, and because these answers are quite common in the metagame regardless of Dracovish usage (If you want proof, look at SPL logs) I do not believe Dracovish is very centralizing (Unlike Corviknight) and, due to the myriad of ways to defeat it with better play, do not consider your argument as to it's potential ban as valid and would strongly oppose its removal from OU.