I think the problem can be summed up as: Jason who?
For all the fun we make of his accent and wooden acting, Arnold Schwarzenegger is a charismatic actor. He made the role work. Take him out of the picture (literally) and you’re not left with enough to make a good movie.
It also had George Maharis, Richard Moll (Bull from Night Court!) as the Sorceror Xusia and Joe Regalbuto (Frank Fontana from Murphy Brown!) as Darius.
Much like the OP, at about the hour point I found myself so uninterested in the movie that I turned it off. This is pretty rare for me, as I’ll sit through most movies and shows I don’t like (my fiancé’s addiction to Real Housewives of “X” type shows excluded).
I loved Arnold’s Conan, the first movie. From the opening, through Conan rising in the fighting pits/games, to discovering his father’s sword, and of course James Earl Jones - all great stuff. The second was pure camp and not something I’d re-watch.