>>2847029>how the failure occurredi realized while i typed the question yesterday that the problem is that you are descending on rope vs rope, instead of rope against metal. in that incident you mention, the friction hitch failed probably because it heated up and eventually melted. avoiding having 2 ropes rub against each other in any part of the system is a basic thing they always teach
but other than that i think it's actually a valid system, it's good to know just in case. although if you are going to do that, you might as well attach the friction hitch to both threads instead
and in any case it's better to learn how to do the rappel on 2 carabiners thing, it's i guess safer and you probably always will have 2 carabiners available