Hi I'm here to break down this argument with a long post. Note that I haven't laddered competitively in months, but I have played the ladder on occasion casually when I'm bored so here we goHi MAMP i agree with all you said, and i think we should suspect test Shit Gear Primal Groudon as well since it's so broken imo because:
First I'd like to ask a very simple question: Who uses thunder wave when glare is superior in every way besides fulfilling some sort of niche? While being immune to burns is an issue, being immune to water attacks actually isn't as much of an issue as you may think. Earth Power bops it, for instance, and while it's deceptively bulky, it's still not going to be taking special attacks that well (Aerilate MRay Boomburst anyone?)-it's immune to thunder wave, burns and water attacks
So do other mons like Mega-ttar (PH also has that benefit of psuedo-status immunity too!) and MMX (which can run an item), but nobody complains about those. I get that PDon does have the next point going for it, but come on.-has incredibly high stats boosted by shift gear, boosting its attack to insanely levels and outspeeds almost anything after 1 single shif gear
While I do admit you have somewhat of a point there because Desolate Land V-create hits stupidly hard, Flash Fire and Primordial Sea say hi nonetheless. Sturdinja can also take V-creates for years and stall out Sacred Fire with Lumcycle (this ofc requires team support to keep hazards off and for PDon to not have Magma Storm, but this means it either loses access to Ground STAB or loses access to healing/some other 4th move on a shift gear set).-has access to the devastating move V-Create and even Sacred Fire, that boosted by the sun and used with its power nearly OHKO's half of the meta and 2 OHKO's the other half even at +0
-has access to the defenseless move Thousand Arrows that hits flying types, through levitate, has no contact and has high power after a single shift gear

Hi, I'm imposter chansey. Prepare to get swept if you run Arrows because you don't have anything that can really take it on if you set up while I can freely.
In all seriousness, Arrows is actually weaker than you think it is.
+1 252+ Atk Primal Groudon Thousand Arrows vs. 0 HP / 4 Def Mega Rayquaza: 309-364 (88 - 103.7%) -- 25% chance to OHKO
Sure adamant can OHKO an MRay at +1, but it's a roll that isn't in your favor. You should really be clicking V-Create against it anyway but that's besides the point. You're really only hitting Flash Fires with it, but at that point shouldn't you just be running Precipice to hit them harder?
And if you think I'm joking about the Imposter Chansey bit...
+1 252+ Atk Primal Groudon Thousand Arrows vs. +1 248 HP / 0 Def Primal Groudon (250 base HP): 276-326 (39.2 - 46.3%) -- guaranteed 3HKO (A safe switchin to a +1 PDon barring a crit!)
+1 252+ Atk Primal Groudon Precipice Blades vs. +1 248 HP / 0 Def Primal Groudon (250 base HP): 366-432 (52 - 61.4%) -- guaranteed 2HKO (Not anymore it isn't!)
This really does make a big difference. If you're smart, you won't set up until Chansey's dead, but that results in you getting walled by Gira. And I mean any gira, as shown below.
Now, if this were the pre-primal ban meta, I'd agree, but without +1...-forces us to use a Fur Coat Giratina or Mega Latias to wall it, that's just a wasted teamslot because its a mon just for groudon.
252+ Atk Primal Groudon V-create vs. 8 HP / 252+ Def Giratina in Harsh Sunshine: 196-231 (44.2 - 52.1%) -- guaranteed 3HKO after Leftovers recovery
V-create in sun is your strongest move vs gira, and gira tanks it. If you set up, it can tank one and phase you out or topsy you. This is especially true for Prankster Tina.
Something else I'd like to add is that Fur Coat Tina is actually a good mon that can accomplish a variety of roles besides just dealing with PDon. Hell if you want support you just run Tina in general if you can fit it in. As for those people who actually run Latias-Mega, need I remind you of its impressive special bulk and power with Soul Dew? +1 in both offense and defense is not something to mess around with.
-recovers 2/3 HP in sun with synthesis
There's also the issue of Shift Gear PDon being a very complex ban (Shift Gear + Red Orb + Groudon) but if Red Orb's what's being banned, I'm gonna still have to disagree as Red Orb is manageable. I mean, I fought teams with SG PDon on them with a team of gimmicks and I still won, so that means something right?
The last thing I'd like to address actually made me chuckle a bit.
-nearly 80% of people depend on don to win.

Sure thing, buddy.