Well, they do...
Maybe. Maybe not. "Ruined" implies a loss. What has been lost in Star Trek?
I wouldn't go so far as to say STAR TREK has been ruined in the current era, but I do feel like it has lost something.
Bottle shows, as an example I mentioned above. The nature of the season arcs don't allow for them anymore, and it's a shame because we got some truly great character stories from bottle episodes in the past, both for regulars and secondary/recurring characters.
Also, a sense of adventure has been lost in favor of the season long threat. Granted, TNG, DS9, and VGR lost it later in those shows' lifetime, but they all had some wonderful bottle shows or great secondary characters to fall back on. (DS9 especially in that regard.) You can have an episode devoted to a single character and be engaged fully... like
"The Inner Light",
"Frame of Mind", "THE VISITOR", "MELD", "COUNTERPOINT", etc. And ENTERPRISE, for all the faults of the first two seasons, did bring back that true spirit of awe and adventure that was lacking for years before it premiered.
All that being said, the current era DOES have the spirit of the franchise there, such as how DISCO proved in season 4's finale. (While the arc was not the best, it
was the best finale of DISCO to date.) There's great messages in DISCO and PICARD, which is something that the franchise has always been about.
Think of it like this... in some video games, you have the primary mission/goal but there are a lot of side quests that are a great deal of fun. Many times, those side quests
enhance the overall story and appreciation of the game. I look at shows the same way.
Perfect example of doing it right... SUPERNATURAL. Each season had its own major arc, and episodes within the season followed on it, but there were plenty of side stories that were not only a lot of fun, but ended up being among the BEST of the show.
Speaking of fun, that's another thing that feels lost in the current live action era... a sense of fun. You'll never get another
"Captain's Holiday", "Qpid", "A Fistful of Datas", "BADDA-BING, BADDA-BANG", "BRIDE OF CHAOTICA!", or the like again because of how seasons are made now. Give the characters a chance to breathe and enjoy being those characters for an episode or two.
It's quite telling that in the current game being played in the General section, 'Most Disliked Comedic/Light-hearted Episode', Sakonna and I couldn't come up with a
single one from DISCO or PICARD, and that's over 70 episodes.