Hi,
Re: Inflator hose and velcro: Completely variable depending on BC configuration, how it fits you, and how you use it.
For my part, on the two BCs I own (Scubapro Knighthawk, Oceanic Islander), I usually use the velcro, though somewhat "loosely" (just overlapping nap and hooks an inch or less). This keeps the hose somewhat better trimmed and to hand when diving, and I can vent just fine when required. I also pull it out of the velcro for final ascent, as the full hose extension is helpful for getting that last bit of air out of the bladder. Note that just a loose fastening of the velcro allows the hose to be pulled free with little effort at any time, without fiddling with the velcro strap ... sorta the best of both.
There was a rental BC I once used where the velcro was quite low on the shoulder strap, and I didn't fasten it. I was not putting much air in the BC, and it didn't vent well when fastened.
Both my BCs have the "pull dump" hose feature. I have rarely used it, it is a less controlled release of air than the inflator hose. I think I can recall using it only twice, when I happened to be working on something else with my hands in a head-up position, but needed a quick buoyancy adjustment. Convenient to have it then. I generally find that using any of the dump valves (instead of hose) lets more water into the BC bladder, so tend to avoid that.
So, as with many questions, the answer is ... "it depends" ;-).
--
Re: Instructors ... Sorry to hear about such experiences. While not a scuba instructor, I have been an instructor in other things.
Being good at something and being a good teacher of that are very distinct skills, and I fear the latter is much rarer than the former.
However, your experiences definitely cross the line from lack of skill to outright incompetance and failure to meet even the basic criteria of simple civility and appropriate treatment of a paying customer.
I would be livid, and would seek satisfaction and to ensure the poor service reaped negative consquences for the instructors. I would probably invest of my time and effort to that end out of proportion to any reasonable response, that being one of my character "challenges" (don't like to see people get away with that sort of thing)!
Hope you both have a better time of things going forward,
Cheers,
Walter