I would sort-of argue by TNG's seventh season the "writing was on the wall" -and already had been in the sixth season in fact- and everyone knew TNG would end and move to films. Because of this most of TNG's stronger writers either moved to DS9 or simply moved on completely leaving TNG with, well, a rather limited writing staff which is why the writing is so lame in TNG's final season. Brannon Braga who is pretty good and coming up with stories is best when someone who is a better writer is over him. A couple of TNG's better episodes in S3 (like Yesterday's Enterprise) is partly his work but it gets filtered through the better writers (like Piller) and it becomes a fine episode.
Braga on his own? We get crap like "Genesis" which makes no sense, throws any attempt TNG made at making some-kind-of logical sense when it came to its premise and "science" out the window and is just an episodic shock fest with everyone all happy at the end as if nothing horrific had just happened like someone's face being burned off by acidic venom and needing to be reconstructed or the consequences of civilians and children being on the ship. Not to mention that the "virus" was fairly easily caused by a simple mistake by Crusher.
Ugh.
Jeri Taylor is another writer who's work mostly came through more in the seventh season (and through Voyager) and she is someone whose writing I'm not a fan of, her stories can tend to be very "women centric" and not that that is a bad thing but they can greatly feel that way so we get episodes that feel like grocery store romance novels (Sub Rosa.)
Anyway, with the stronger writers on TNG either moved to DS9, working on the movie or moving on completely that left TNG with not much to go with. Had they felt the need to continue to do TNG the better writers may not have moved on and TNG wouldn't have had such a lack luster seventh season.
At the same time Berman was also taking a much more safer, blander, "Trek as a product" approach to TNG which also really softened the series during its last couple of years. (Him being against story arcs being a big part of this.)
TNG's final season wouldn't have been such a mess if it wasn't decided it was going to be the last one (but the decision did need to be made in order to give it a proper ending) and if Berman wasn't such a corporate asshole who wanted to play it safe in order to line his ass with money.