Alcohol vs synthehol. That sums it up for me.
I think there's something in this.
Of the original Trek shows, only TOS presented us with human characters who were close enough to the audience to be relatable, but still far enough away to be plausibly futuristic.
(ENT came next closest, but maybe they made their humans too "modern" and "fallible", and not evolved enough..... which was kind of the whole point of the show, I know.)
The TNG crew were far too 'perfect' in that regard. They were futuristic space people, full of their own morals and the ways they had evolved from the past, especially in Season 1. They generally lacked relatable human foibles. Some of them faltered at times, some of them suffered real problems. But there was always a sense of the false about them. They were, in essence, more 'fictional' than their TOS forebears.
(DS9 and VOY both made attempts to show flawed humans, but they were constricted in many other ways that TOS was not. I'll allow that DS9 probably presented us with 24th century Trek's most realistic characters, human flaws and all.)