Well, i can remember that in wow dungeons there was way more shit talk. Also there is no mythic+, which is the last time i played the biggest source of toxicity in WoW.
Still 2 things that stand out:
I saw way more flamewars in WoWs LFG (raids) than ever in FFXIV PF - that may be because GMs are very strict when it comes to language and people rather avoid that, and NOT because they are nicer people - still, i only encountered one flamer in PF in 3 years.
Also, the noob (sprout experience) - most people are really friendly to sprouts and help them with tips. Again, other MMOs also have their care-bears - but the sprout icon alone stands out.
So i'd argue, that people are people - everywhere - but the environment can shape behavior. And FF14 and their stuff definitely pushes the player way stronger in that direction than others (which of course leads to a (limited) self selection of players - there are players that cannot play with these rules and they will quit - players looking for a safespace will rather join, etc.).
So no, i don't think the FF14 has better or nicer people, but the game design and the gms push it more in that direction.