Maybe not iMovie, but I've been having great fun with the 'Memories' feature in iOS 10. I used it to make a 4min video of our recent family holiday in 30min on the plane. - Imported photos from our waterproof camera (compact-style, not GoPro. Cheaper than GoPro!) via the Apple Camera Connector. - Used mainly photos from the iPhone, but because I have Live Photos turned on, it was the 6-sec video that got put into the final clip instead of just the still.

I agree with your premise; the hard part is definitely finding the interesting bits. Actually putting them together is easy after that. There's some good stuff happening with "exciting moment detection" based on other sensors; like peak heart-rate and speed if you record those on Garmin.