There's still a sizable portion of the casual audience that perceives her that way. I don't think Jean is underrated among X-fans in particular, comics fans in general - rather, Marvel has botched her return as far as I'm concerned. Teen Jean kept the genuine Jean from returning at best and denigrated her character at worst, and Phoenix Resurrection and X-Men: Red both had a few problems, with Red in particular seemingly completely superfluous.
Jean has a reputation of being part of the love triangle involving Scott and Logan rilvary (wicth is of coursre blown over proportion) or being the woman that died a lot for being the Phoenix, these last few years after her death also gave him the Gwen Stacy syndrome, that is not a good thing frankly and whole generation of fans don't seem to care for her.
"Wow. You made Spider-Man sad, congratulations. I stabbed The Hulk last week"
Wolverine, Venom Annual # 1 (2018)
Nobody does it better by Jeff Loveness
"I am Thou, Thou Art I"
Persona
Jean got screwed up badly when she died. No wonder the decision was to bring back Jeen first, the character really need a detox period. Jeen showed that Jean could be cool again and put in perpective the character.
No wonder writers that grew reading Morrison, whedon runs despise Jean
If it makes you feel any better, Jean's coming off of her highest publication year ever in 2018, beating out '92, '93 and '96.
There's definitely some differences of opinion when it comes to Jean. I think there's a tendency to write her as a little too perfect and upright. She tends to succeed at everything she tries. This makes it difficult for creators to add much complexity and puts her at risk of being portrayed as rather dull. Of course she has a lot of potential for complexity, and a deep dark side, but I think writers in general are afraid of shaking her up too much. Morrison did takes some risks with her but it didn't all pan out. Bendis' also took some risks with Jeen but when compared to her older depictions of being the same age, she really came off as juvenile and reckless.
It's a balancing act for sure, trying to keep Jean interesting while still staying true to her more bedrock characteristics. I think this is part of why it's such a temptation for creators to use Jean with the Phoenix Force. For Jean the PF is a literary "get out of jail free card" for cutting lose emotionally and embracing everything that we know is bubbling just below the surface of her calm and empathetic personality. Jean's dark and deeply passionate side is only glimpsed occasional when she's separated from the PF.
Jeen is probably the reason adult jean is back. she breath new life to the character