> I also dislike having to wait a few seconds upon starting/resuming a video for the controls to fade away.
I get the annoyance, but especially on mobile, it conversely helps if you want to advance the video by as few frames as possible to catch a freeze-frame gag or something like that. If the UI immediately disappeared upon resume, you'd have to triple tap to immediately pause the video again. (On desktop you can just mash the keyboard or even use a dedicated "advance one frame" key, but on mobile that's not available.)
I sometimes use a Bluetooth speaker on mobile just so I have a pause button handy. Playing a video full screen requires me to tap once to bring up the controls, and then again to pause.
I get the annoyance, but especially on mobile, it conversely helps if you want to advance the video by as few frames as possible to catch a freeze-frame gag or something like that. If the UI immediately disappeared upon resume, you'd have to triple tap to immediately pause the video again. (On desktop you can just mash the keyboard or even use a dedicated "advance one frame" key, but on mobile that's not available.)