What specifically makes most of the stories on Star Trek: The Next Generation "Non-SciFi" stories in your estimation?
Most of the TNG stories have nothing to do with exploring new ideas, which is the essence of SciFi. Heck, the opening credits say they are going to "explore new life," but how often did they meet any aliens who are actually based on any new idea?
Most of TNG's stories are just soap opera/political drama-style regurgitations of cliche human problems that occur in the real world. For the most part, the aliens on TNG might as well be humans, because if they were, it would make no difference to the story.
When they are not regurgitating real-life human problems, they instead present filler about extremely-human-like aliens of the week and/or space disease taking over the ship. Or holodeck filler that regurgitates detective book/film and Western cliches and/or Mark Twain stories, etc. Where's the SciFi in that?
TOS also had stories about the ship being taken over, but unlike TNG's, TOS's were done in original and creative ways fitting for the SciFi genre, like with the Nomad droid or Salt Vampire, etc.
TOS didn't even have that much "internal conflict", it was always their reaction to how to deal with external situations that led to conflict. It wasn't like they just were always at each others' throats when they weren't on missions.
TNG was more or less the same.
Whether there was a lot of internal conflict when "they aren't on missions" is a moot point, because over 90% of the screen-time deals with mission-related problems.
TNG also spends that vast majority of its screen-time dealing with mission-related problems, during which the characters recite bland, generic and interchangeable dialogue wherein they all agree with each other.
In contrast, the TOS characters fight with each other, using unique speech patterns with non-interchangeable dialogue, which is far more entertaining and artistically interesting than TNG's version.
TOS only had three central characters to focus each story on, and those same three characters were also a Freudian Trio (Id, Ego, Superego). It 's easier to write episodes only about those three when they also functionally work as one character unit, opposed to TNG's more ensemble based cast.
TOS is much harder to write for, because each of those three characters makes a unique and useful contribution to the show.
On TNG, they can just write blurbs of dialogue, divide it up into random portions, then randomly dole those portions out to any character. That is very easy to write.
On TNG, it rarely matters who they give the dialogue to, because most of the characters on the bridge serve no useful function there, and the comments/functions they perform are interchangable with other characters who are also on the bridge at the same time. I.e. Wesley, Riker, Picard (Picard is a redundant character if Riker is on the bridge, and vice versa) Worf, Troi, etc.
To be a
successful ensemble, the TNG writers would have to make each character serve a unique and necessary purpose, as do the characters on TOS. As it stands, the TNG ensemble is tantamount to one or two characters, who have their dialogues randomly dispersed amongst 6-8 redundant bodies.
In other words, the number of different names and bodies gives TNG the superficial appearance of being an ensemble, but the lack of a unique identity & personality & function among each of those characters means that they do not actually do what a properly-written ensemble does.
