So after such a long, long wait, Strava has finally rolled out photo uploading from the PC web interface. It's only been... what, 2+ years?
HIP HIP HOORAY!! /sarcasm
Anyways... tried it just now. Mostly works, but occasionally buggy where you drag a bunch of photos and 1 or 2 of them inexplicably fail to upload, disappearing from the upload box without any notification. Easy enough to workaround it by dragging images one at a time, giving approx. 3-5s in between (usually the drop happens within that time) so you can identify and re-drag the dropped image. Doesn't make it any less annoying though.
But who am I to complain? At least they finally catered to us minority users who don't use a smartphone (or Instagram) to upload, eh?