When I say she was mishandled in the 80s I mean basically the whole incident which led to Roger Stern resigning/getting fired from Avengers. I thought in context that was pretty obvious, obviously before that happened Monica was at the height of her popularity and prominence.
I don't think the point of Galactic Storm was to make Steve look incompetent, though there was definitely a lot of questioning of his, hmmm, by the book heroism in the edgy 90s. But you get to a point where all the characters look murky and poorly written because of plots like The Crossing. Some of the super self-righteous Steve stuff that played into Galactic Storm was set up when Gruenwald did the "Steve never killed even in WW2" retcon, which has since been pretty much dropped from the character. I don't think Gruenwald did that to make Steve look bad, even if it reads goofy today. Similarly the John Walker as replacement Cap wasn't meant to show Steve as outmoded; it plays with that idea in order to reject it. Where Steve did get screwed over in the 90s was with the cancellation of the Mark Waid run for the infamous Liefeld Heroes Reborn volume.
I don't have actual evidence for this, just impressions from comics I haven't read in a while, but my guess as to why Carol didn't get the Captain Marvel codename immediately after Mar-Vell's death is because Claremont felt Carol's heroic journey that led to her becoming Binary (and thus having her own unique cosmic powers/codename) was more satisfying/progressive than her taking up someone else's legacy. I think you can argue about whether that was the right choice in retrospect.