Hmm... I'd say it has more than one episode's worth of plot, though maybe not four (and certainly not four in modern terms). I had to remind myself that this was before The Five Doctors so the Time Lord side of things wasn't quite as rinse-and-repeat as it was to come. While The Deadly Assassin does Time Lord politics far better, Arc of Infinity puts at least a little effort into differentiating them and giving them various points of view.

None of these account for random teenager enthusiasm for episode 4, but there you go.