Is it possible that you inadvertently changed the Sharpness setting on your camera? (Inside the DJI app on your iPhone/android) For that matter, you might have switched to 720p in the app. Even changing the frame rate, iso, etc can all cause softness (but I suspect you already know all this).
Its also possible that you did something in iMovie. Have you opened up your original source footage in Quicktime Player and compared it to your iMovie output? (Or compared your source footage from Craigmore to the source video from other locations.)
In iMovie I don't think there is a way to directly adjust "sharpness", but you can try something like adding a "Hard Light" video effect, and then dial back some of the effects of Hard Light by adjusting the sliders under Color Correction. I highly doubt you will get results that you like. You might want to consider taking the leap to Final Cut.
Or if you have Photoshop, you can actually use all of Photoshops image correction tools (and filters) on a video. You just need to open the video in photoshop (a timeline will appear at the bottom) and then convert the video layer to a smart object (critical step). Then adjust away. (You can even remove the fish-eye effect in photoshop).
