How to Classify THE HIGH AND MIGHTY

I was hoping we'd see the return of the theater manager's rating system!

I think you're right that a lot of the problem was with the script, which Gann adapted from his own book. An author, particularly a wordy one, adapting their own work as a film script can sometimes lead to problems if they're too in love with their own words and forget that movies are just as much a visual medium. And the characters are basically stock types, retrofitted to flesh out a preconceived storyline, which often seems to happen with "adventure" writers. I've seen the other two you mentioned, but too long ago to make any real comparisons. The one THATM makes me think of is The Crowded Sky (1960), with Efram Zimbalist Jr. as the pilot with a haunted past and a planeful of similarly one-dimensional characters. On THATM, I think it was John Wayne's production company, still in its early stages, so he may have done some tinkering? It was also in the early days of CinemaScope and Hollywood was still learning how to make those cameras mobile, so maybe Wellman ran into problems with that?