I think Star Trek
holds up well even now. Certainly, compared to science fiction shows like Babylon 5
(which I just rewatched recently), Trek's plots strike me as well-paced and most of the episodes are devoted to plot rather than beauty shots of the ship or CG imagery of ships, planets, or cities.
In sum, I don't agree with any of the OP's observations and I think TOS holds up very well, no matter its age.