I am a pretty inexperienced diver, but I have no trouble at all taking off and refitting my mask - wouldn't think twice about it now. When I did it at 7m in the OW class, which was just a few dives ago really, it was a really big thing. Had I panicked and gone runaway at 16m I could have seriously hurt myself. The second time I tried it it wasn't such a big thing at all, mainly because I understood that having done it once, I could do it again as I knew what to expect. It is, I think, for most trainees a very stressful thing to have to do first time, and as such should be treated a bit more cautiously than seems to have happened in this particular instance. Sure, once you are qualified OW you can dive to 18m and as such you should be able to do all the things you learnt in OW at that depth, but not the first time, surely - it's like expecting a learner driver to be able to drive at 70mph on the motorway in the morning rush hour on their second lesson.
Jeff