The first time they introduced the Eugenics Wars set in the 1990s, Spock called it the last world war. Pike in SNW elaborated that it was part of the escalating conflict that went nuclear as WW3 decades later.
transwarp
I'd say TNG mostly stopped exploring new frontiers halfway through season 1. Farpoint promised exploration, but soon the ship is ferrying diplomats and scientists and answering Federation distress calls. The worlds are new to the audience, but not the characters.
He wrote a book about making it. The section on studio interference implies that it was all egregious, but it lists Paramount trying to fix most of the problems that were still in the final film.
She directed episodes of both "Enterprise" and Star Trek: Enterprise", which each lasted two seasons. The stealth name change was surprising back then.
The idea was that the Klingons had joined the Federation and we'd see Klingon Starfleet personnel in the background. When they did add Worf, he was to be more frequently Data's relief than Yar's.
If you read the initial material, Data is drastically different. There is no explicit mention of being unemotional, just that he tends to speak more formally. He's supposed to be more like the Ilia probe than Spock.
Worf didn't exist at first, so Geordi the teacher with bionic vision would be the most "other" character. If they'd seen any of the early press material for Phase II, Spock's replacement there was a very junior officer.
There was a spinoff pitched during TOS called Hopeship featuring M'benga. The pitch for NBC/RCA was that instead of introducing expensive colorful sets, they could stay shipboard and have expensive alien makeup and costumes.
A Quality of Mercy also showed Una in prison, and Those Old Scientists implied she's revered. Did sending that letter prevent Pike from recruiting her lawyer? Things are already not heading down the exact timeline we saw Ortegas alive in.
It's definitely an industry change. Frakes has talked about how when he directs an episode now, the show's director of photography tells him to keep the camera moving.
Wesley's mom, a main character, was initially going to be the ship's teacher. They shifted her over to the empty doctor position without changing much about her. Then they made a new teacher who was also changed to be a bridge character, as the ship's pilot.
While Riker and Troi are adapted from Decker and Ilea, Beverly was more extrapolated from yeomen Colt, Smith, and Rand.
Edit: specifically, their bios were mostly about a potential relationship with the captain, how competent they were (making them reasonable mates for him), and having the "walk of a striptease queen."
TOS had a proposed spin off for him, which would have ended up about his brother (played by the same actor) as first officer of a medical ship.
It would be astoundingly different after SNW.
She played the captain of the Lakota later in DS9, Captain Benteen.