Kacper - is your boat a fractional or masthead sloop? You gotta be careful in high winds with just a lot of headsail and a masthead rig, that can place unnatural balance on your standing rig. (I'm sure plenty of people will disagree with this point) Also, masthead rigs are not as good as fractional rigs sailing on just the main ( again, room for discussion). Of course I have a masthead sloop...
Regarding the shape of a large genny when reefed the bigger problem is a higher center of effort I think, not just bad shape due to awkward sheet angle. It's as if you are attaching the tack 3 feet or more off the deck, moving the forces of the sail higher. This causes your boat to heel more and have less efficient forward thrust, which cascades to other problems.
I think your failure was to not reduce sail before the wind got out of hand, but I guess you just chalk that up to experience eh? "D I think the rule of thumb for us beginners is if anyone on the boat thinks the word 'reef' it's time to do it.
A lot of time if the weather report is predicting winds over 10 knots I'll just reef the main at the dock.
I'm a wus but then again when the real men are flailing around madly on the foredeck with their wives screaming at them to not die I'm safely in the cockpit making sure my coffee doesn't spill. :P