I think the difference is mainly in how TNG defined the ensemble cast, with each character having episodes center around them. In doing so, they did keep it relatively fair in dispersal throughout its run, but by the end leaned toward what were the more interesting characters, Picard, Data, & Worf.
This was an almost complete departure from the TOS format. No one but perhaps Spock & Kirk had entire episodes center around themselves alone, with an exception or two, & by far character centered episodes were really rare, in those 3 seasons
In a way, this is one of the reasons TOS made for a better movie dynamic. The characters were still rather unexplored & had a simpler relative dynamic between them, compared to TNG who fleshed out all their characters, over 7 seasons, & when transferring them to the big screen, characters got completely stripped of their worth or refit into something they had never been, because were they to tell a story that actually featured the characters as they had been developed, there'd be no real room for it to be an action story
TNG was very much a sci-fi soap opera mixed with action & suspense. Not so much the same mix on TOS