It's true though. Sanji fans downplay Jimbei the way Zoro fans downplayed Sanji.
You're conflating a lot of tings and making a lot of false claims here.
First and foremost Sanji fans are not the only ones that clown Jinbe, some Zoro fans do as well as other neutral fanbases.
So this Sanji fans hate/downplay Jinbe coz xxx is a false flag.
Zoro Fans: "See the Supernovas? Sanji doesn't belong here. What do you mean the Monster Trio is a thing?"
Sanji Fans: "See the Monster Trio? Jimbei doesn't belong here. What do you mean the billion bounty club is a thing?"
I'm not sure what this comparison is supposed to be the Supernova and the Monster Trio are completely different concepts. One is a concept that was established based on a 100mil bounty threshold all the way back on Shabondy pre-ts. Irregardless of how strong Sanji is, he cannot become a Supernova. Regardless Sanji has long proven to be much stronger than the lot of the supernova so that title has no bearing on how strong Sanji is, whereas with the Monster Trio is quite literally the title for the strongest SHs, to which Jinbe can lay claim to whenever he wants and force it into the monster quartet if he proves to be strong enough to do so. If Jinbe is unable to force himself into monster trio or force it into the monster quartet like tons of powerful additions to the SHs in the likes of Robin or Franky and failed to do then it just means that Jinbe is simply not strong enough to do so.
Moreover the billion bounty club is a ting but it has not relation to the "monster trio". Jack is also part of the million dollar club for instance you think he breaks the monster trio or forces it into the monster quartet?
Zoro Fans: "Lol. Did you see Sanji's fail against Doflamingo [who used hax]?"
Sanji Fans: "Lol. Did you see Jimbei fail against Gunko [who used hax]?"
Can't speak for all Sanji fans but from my perspective, Jinbe losing to Gunko's hax is whatever. In the first place Gunko is commander level and maybe even potentially even top commander level so Jinbe losing to a character of that ilk isn't really a big deal to me. That said however, his lack of effort and utter useless even in the face of the dire situation in front of him is a massive L and worthy of criticism. Losing to hax is not a big deal, even Luffy loses to hax from time to time.
Zoro Fans: "Hehehe! Sanji said, 'save me Robin.'"
Sanji Fans: "Hehehe! Nami called Jimbei out for being weak."
This is also an apples to orange comparison.
Nami calling out Jinbe for being weak is quite literally the nail in the coffin for monster quartet advocates like yourself as it implies that even as strong as he is, he doesn't quite measure up to the monster trio.
Where as the Sanji Robin ting ironically enough was the what actually birthed the title "wings of the pirate king" title in the manga

and further solidified Sanji's position in the monster trio as well as his relativity to Zoro.
If you gave the Sanji detractors that mocked him for doing so the ability to chose whether or not that scene happened, reckon they'd opt for the latter given the consequences of it lol
There is reason why the Zoro fans that mock Sanji for that are Zoro fans and I'm a Sanji fan for instance, I'm able to appreciate moments of characterization like that from characters. 'I'm useless in the current situation due to my inability to hit women but I'm lucky enough to have strong nakama that can help cover for such weakness', I don't know about you from a Sanji/Robin standpoint that is pretty dope scene.