One thing I do think should be iterated for Wellspring is that the Mask not only provides a free power boost to literally all its damage, but also means Knock Off doesn't make progress against it from Utility Mons vs attackers. The trade-off has been noted in not allowing Boots to alleviate a Hazard problem, but it's not exactly a strict negative that you just have to accept when playing Ogerpon.
252 Atk Wellspring Mask Ogerpon-Wellspring Ivy Cudgel vs. 0 HP / 0 Def Mew: 186-219 (54.5 - 64.2%) -- guaranteed 2HKO
252 Atk Iron Valiant Close Combat vs. 0 HP / 0 Def Manaphy: 196-232 (57.4 - 68%) -- guaranteed 2HKO
Bearing in mind that Iron Valiant has a bit of Base ATK and 20 BP over Ogerpon's Ivy Cudgel here, as far as just raw numbers, while Oger's moves are always Consequence-free for it to land in-and-of-themselves.
This is where I consider the Dragonite comparison particularly flimsy, because that mon lives and dies by its item AND Tera to optimize Multiscale, set-up turns, and damage from its otherwise non-STAB priority. Compromise any of these resources and Dragonite becomes significantly harder to play compared to an Ogerpon lacking any of them (excepting the item comparison for obvious reason).
That one-time easy speed control really only applies to 1 or maybe 2 if we count The Jug. Even then Iron Valiant often just uses that free speed to set up sweep. There’s an obvious pattern with Booster Energy, and its use in OU. Majority of the Pokemon that use it as an aid to sweep. Either to gain the speed needed, or additional fire power to muscle through Pokemon that would other be checks. Even Iron Treads, who isn’t a set up sweeper, only uses booster to facilitate other Pokemon to sweep via suicide lead.
I’d argue that practically no OU viable mon uses the item for purely fair purposes. Gone are the days of Scream Tail, and Iron Jug is holding by a thread. The fact that even Iron Valiant uses Booster more so as a sweeping tool rather than an anti sweeper tool says a lot. I fail to see how this is healthy for the game.
This is just a consequence of the item's one-time-use nature that it was designed around (trading the item slot and a fleeting buff for not needing specific team support), which invariably favors using it to make a pivotal play rather than prolonged action (also see Lures with the resist berries, Focus Sash on Suicide Leads to ensure Hazards, or just Unburden in general as an ability). Playing a mon like IV to aggressively go for a Sweep is just a more efficient use of Booster Energy than reacting to a Speed-control need since you can't do that repeatedly with it if the opponent can (such as an aggressive Scarfer or being able to set-up in multiple instances), and if it's not a healthy dynamic that falls more on the offensive traits that allow Valiant to turn 1 round into a Sweep with its huge mixed offenses, coverage and set-up move options across sets. Many items exist that inherently favor a particular method of play, and the users/abusers will be those with kits tailored to that style.
Neither of those mons are OU though. If I'm dumpster diving just to check it, might be time for a conversation.
Like I get it, Ogerpon-W isn't cracked vs. HO which is all people run these days. But if one wants to run non-HO, the mon is cracked out.
Has to be noted for one thing that Grasspon is very well ranked in the tier (Strong Grasses offer quite a bit in this Meta), the largest reason it's not OU by usage probably lies in the fact that it's mutually exclusive from Wellspring, which obviously is a very widespread Pokemon. Citing that the mon is not OU by usage should not matter as much as discussing if the Pokemon can put in work beyond the discussed match-up (see Bronzong into Kyurem).
Going to add an endorsement for Sinistcha to the conversation for the same reason, also serving as a good Ground check, Spin-blocker, and Win Condition depending on the set, while being a particularly useful Wellspring answer as long as Play Rough is its standard for all the Dragons. Matcha Gotcha threatens a burn and drain (undoing progress against a fast-paced power mon that already hates Chip) while Strength Sap provides healing and stops momentum from ANYTHING Physical both present or switched in, while different sets can further exploit it with Calm Mind to set-up and Foul Play to Punish a SD as long as you're in decent health.
+2 252 Atk Wellspring Mask Tera Water Ogerpon-Wellspring-Tera Ivy Cudgel vs. 252 HP / 160+ Def Sinistcha: 185-218 (53.4 - 63%) -- guaranteed 2HKO
+2 252 Atk Sinistcha Foul Play vs. 0 HP / 0 Def Ogerpon-Wellspring: 226-267 (75 - 88.7%) -- guaranteed 2HKO
While I'm singing Sinistcha's praises, SD Gliscor absolutely DESPISES this thing, and Defensive/Spikes sets only have Toxic to throw at it (so if it absorbs a status or you REALLY hate Gliscor and tech in Substitute maybe). Given one of the styles Gliscor seems to exploit the hardest is Bulky teams and Fat Balance that can't pressure it, Sinistcha might do well for play into it along with Wellspring as another concerning breaker.