Hm. Lets imagine (just for a second) there was no DOS and DOS2. Would BG3 being a standalone project alter your perception? Would you see its story (the bits we know about now) as mediocre? When I was first playing BG3 I did find the story very engaging, I can't name a major flaw in the storytelling without inventing it and purposefully squeezing it out of myself

It's a bit of a pointless endeavour asking if the perception of BG3 would be different were it a standalone project as it isn't, but just to play along I can categorically state I would still find the companions unbearable and poorly written and the story left me totally uninterested. Subjective takes of course because half the fanbase is salivating over Astarion ad nauseam.
Haven't played for almost 2 years but I do recall some pretty glaring flaws in the story, the main culprit being informed at every opportunity that you must rush to seek a cure for the tadpole immediately but then leisurely being able to go about your business with no consequences.
Why can a Vampire spawn walk in the daylight? Apparently because of the tadpole.
Why are all these companions with their extraordinary backgrounds and tales of great power now level 1? Apparently because of the tadpole. Those are not particularly good examples of writing.
There is also Shadowheart's box that is so integral to the story that somehow it finds its way back to you regardless of whether you kill Shadowheart or choose not to use her as a companion (as far as I know anyway, it might have changed in recent patches?).