Completely agree. Strange new worlds and lower decks are absolutely amazing trek shows, Picard season 3 was pretty good even though I didn't care much for the first 2 seasons and even though discovery is typically the least liked of new trek, it'll always have a special place in my heart since that show is what made me a trek fan in the first place.
I've since watched ALL trek content except for most of TOS and TAS, it's just to old for me. I've watched the most highly recommended episodes but I just can't get into that show and I've tried multiple times.
Eh, somewhat disagree. I think some series have big potentials for spinoffs or side stories. The Disney Star Wars movies were terrible, agreed, but some of the shows are fantastic.
Marvel (and DC for that matter) is finicky. Comic books are, by their nature, extremely continuous, so there will always be more content to adapt. Whether or not it's good or worth adapting is dependent on both the comic series and the producers' capabilities, but that's another issue.
I mean, I'll give an example. The Last Airbender, fantastic show. It could have ended there and we'd all be satisfied. But The Legend of Korra, while not as great as TLA, was still (imo) very good. But the Last Airbender movie? Yeah, we all know it sucked hard.
I wouldn't say writers should never ever look to make spinoffs or side stories to existing content, but obviously it should be good, and it's demonstrably possible. Star Wars gave us The Clone Wars, Breaking Bad gave us Better Call Saul, and I mean on a somewhat relevant note, LotR gave us Shadow of Mordor, which I really liked. New, original content [edit: as a sequel to already existing content] can be good... but obviously, not always.