Eh, a game that drags for more hours than it should and constantly betrays its themes shouldn't score as high to be honest.
Mind you, that's not so much the case with P4 (Not as much as least).
(Also, Zelda is not even an example now. Every recent entry aside from BOTW has scored less than 90, much less in fact).
People may not agree with your takes on how the game handles its themes, that's the thing about literary critique (and adjacent), it's all incredibly subjective. Your read of the game is valid, sure, but so is the read of those people who disagree with you; it just so happens those people appear to be far more numerous than the ones who feel Persona betrays its themes.
The comment about length is, again, an issue specific to certain people; very obviously, given the long term sales of the games, the consistent popularity and excitement surrounding them, and the critical acclaim, the length is not viewed as a detriment by others.
Also, Zelda is very much an example, every new mainline Zelda scores a 93 or above. If you want to count spin offs and rereleases to claim otherwise, then sure, but I can do the same and talk about Persona Arena or Strikers or Dancing or rereleases like 4 Golden and tell you how no Persona release in recent years except P5R was a 90+, and we'd end up in the same place.
Which is to say, arguments about "bias" in critical reviews when selectively applied to one specific property or developer are always disingenuous across the board. If you want to make the case that Persona gets more benefit of the doubt with reviews than many other games – which, by the way, is an absolutely valid thing to say, because it
does – then at least be honest enough and accept that that's not true for just Persona, that's true for
everything. Critics are people, they have their own preferences, those preferences inform their opinions. Popular and beloved IP and developers (Zelda, Mario, GTA, Naughty Dog, Bethesda, Persona, FromSoft) always gets a bit more leeway with reviews and critical acclaim than equivalent other stuff might. Either you accept it across the board, or you accept it for nothing. Trying to claim it applies to Persona but nothing else seems like you have a bone to pick with this specific series in particular and are trying to reconcile the fact that others like these games more than you do, and rather than going with the Occam's Razor explanation of "they just liked it more than me" you are trying to come up with all sorts of contrivances.