You're missing a lot of the TNG story I think, and in particular two people. McFadden left the show because she didn't get along with Maurice Hurley, the lead writer, and Gene's drinking buddy (probably because of the sexist stuff you cited, but probably many other things too). Hurley wasn't all bad (he invented the Borg), but mostly his writing was crap, and you can tell because season 1 was so bad. Hurley left after season 2.
The other person you're missing is Rick Berman. He took over running the show in season 3. He begged McFadden to come back, and is the reason she did. Also notice that season 3 was probably the best of the lot, along with 4 and 5, where he was running things. All the "classic" TNG episodes were made under Berman's supervision. Berman's gotten a lot of flak for stuff (he also went on to work on DS9, VOY, etc.), but he really deserves full credit for turning TNG around and keeping it from sinking, and making it a real gem.
Roddenberry's problem is that he was just like George Lucas: an ideas man, but terrible at execution. He came up with some great high-level ideas for stuff, but when he was too involved in the low-level details, the results were bad. He also apparently sucked at picking good lieutenants. Berman is probably the opposite.