Well I know this is very late but I would like to share my thoughts on Palafin.
It should not have been banned in my opinion.
But in all seriousness this pokemon was really not that bad. While 160 attack and priority is really good it is on a pure water type with somewhat limited coverage options. Both of its main sets are good, but they are extremely vulnerable into Palafin's best counter (and I definitely say counter in this case) Ogerpon Wellspring. Wogerpon itself is rather contentious but possible broken checks broken aside it is just the (almost) perfect counter for Palafin due to its ability water absorb. Plenty of other pokemon get water absorb too of course but unlike all of those pokemon Wogerpon can threaten Palafin offensively with power whip. This still might not seem that bad until you realize that Palafin's best (and pretty much only) way to beat Wogerpon is acrobatics which is a move that requires you not to use an item to reach its full potential which for Palafin is a huge no no. There are ways around this of course (this is where mixed boomburst throat spray sets came from) but it is still a huge problem. Not to mention even if you do get to be able to use acrobatics not only is Wogerpon still faster and can slam you with power whip still but it can also tera water and get rid of its flying weakness meaning all of your work (or sacrifice of an item) was for nothing. This is probably one of the most dominant matchups I have ever seen in if not the whole of competitive singles at least sv.
This dynamic alone probably should have been good enough but of course not every team can/wants to run Wogerpon. Luckily however there are other pokemon in ou that can help. One of the best examples of this is Rillaboom who not only has a priority grass move in grassy glide but also has enough bulk to live even a choice banded wave crash once and cb jet punch around 3 times. There is also Zapdos who can beat Palfin offensively and defensively as it is and bulky electric type who can fire off a strong volt switch/discharge and can punish a lead Palafin by switching in on a baby Palafin using flip turn and (sometimes) give it paralysis thanks to its ability static. This is one of the funniest and most satisfying interactions in gen 9 ou and it is the biggest reason why only choice band Palafin should use flip turn (and even then). Then there is Dragapult which took me personally by surprise. It even tanks choice band wave crash surprisingly well (yes, I know it resists but Dragapult is pretty frail) with it 2hkoing. This leaves Dragapult ways to both annoy and outright kill Palafin such as outright killing it with specs shadow ball or burning it with will o wisp. There is Raging Bolt who quad resists Palafin and has electric sucker punch which means it kos a Palafin locked into wave crash/close combat. Even bulk up sets aren't a big problem since Raging Bolt still easily tanks jet punch and kos back with thunderbolt (or draco meteor depending on if Palafin teras. There is Meowscarada who sucks but can tank a jet punch and beat bulk up sets with its always critting flower trick. Kyurem doesn't take Palafin's fighting coverage particularly well (especially band which can outspeed it) but it easily beats bulk up sets with its subtect set or specs using freeze dry. Dragonite has multiscale and extreme speed so it can set up on all sets (except ice punch on choice band but that doesn't sound good into anything else so I doubt anyone would have used it) and out priority jet punch with a powerful tera normal extreme speed (which only 2hkos both major sets admittedly so you would need to be careful). There is Zamazenta who easily walls Palafin with its iron defense body press set just as it walls almost every other physical threat. The final big one I would like to mention is Dondozo who laughs at even a choice banded close combat and sets up to eventually kill with waterfall (or body press if you aren't afraid of no ghost). There are other checks too that I haven't mentioned such as water absorb Clodsire and Sinistcha but all the ones I have mentioned above are the big ones that usually beats both sets.
Of course, with tera Palafin can send some of these checks into oblivion, but these have their own problems. Steel is a great tera type but it is left vulnerable to fire, fighting, and ground and while fire and ground types aren't particularly threatening, fighting and ground moves are some of the most common coverage types in the game with many pokemon having a fighting or ground type move in their arsenal. There is Fighting which gives close combat/drain punch a boost in power, but it is not great defensively with it being weak to fairy psychic and flying as well as not having many useful resistances (dark resist is kind of nice for Kingambit and other good dark types but it isn't usually very worth it). There is Grass which allows you to resist electric and grass but now you are even more scared of Kyurem (plus now you get revenge killed at low health by Weavile) and are bullied by bulky poison pokemon such as Pecharunt and the more rare but still relevant Okidogi and Vileplume. The final one I would like to mention is my personal favorite Dragon which does make you scared of ice types like tera Grass does, it gives you more resists, a good neutral hitting move in tera blast dragon (which also is more powerful than ice punch except against Dragonite), and while you are scared of fairy types and steel types resist your tera blast, your water and fighting moves help patch this up. However, it isn't perfect as it makes you more vulnerable to faster dragon types (especially Dragapult who laughs in your face) and Wogerpon often runs play rough which easily dispatches it. There are plenty of ways to play around these teras and Palafin isn't really the best tera abuser anyway since it doesn't usually gain much offensively unless you tera Water which doesn't give you any new defensive benefits. Not to mention of course that other pokemon can tera too allowing them to survive Palafins attacks with ease.
Now while Palafin may not be unhealthy there is of course the question of what it contributes to the tier because obviously even if it is healthy if it doesn't bring anything to the tier there is no point in keeping it. However, I would argue there was a couple of really good things it brought to the tier. First off, Gliscor gets destroyed by Palafin as even tera Water can't save it from those choice banded wave crashes once you get it low enough. Even without choice band that 160 attack doesn't pull its punches and jet punch alone can easily end Gliscor's whole career. Of course, Palafin isn't on every team and Gliscor would still be good, but I don't think anyone would even consider Gliscor broken in a meta where Palafin exists. Another great thing Palafin provides is strong water priority in jet punch. Now yes, I know we have like 15 viable priority users in the tier already, but strong water priority allows Palafin to take out a lot of the scariest threats in the tier such as Iron Moth, Tera Fire Kyurem, and Tera Ground Roaring Moon. Water priority, while not as good in this department as extreme speed, also provides great neutral coverage which is always useful in my opinion.
In conclusion, I do not feel Palafin should have been banned. It wasn't unhealthy and it even contributed to the tier. It had plenty of checks/counters and it wasn't that good of a tera abuser. Maybe one day (not any time soon of course like a year or 2 from now) we could get another suspect and maybe it will be ou in gen 10. For now, thank you for reading and I promise not to make any more posts about Palafin unless it is about this one. Have a good day!
