well, could a thief of hope steal possibilities ? and if that IS a thing they can do, than does luck or choices even matter if there is only one single possibility

A Thief of Mind or Life may actually work better to steal Possibilities- Choice and Agency respectively. As we know in Homestuck though, Luck is a thing that actually exists, and Vriska very much steals it to the point where a coin toss that would usually be a 50/50 split, has a 100% chance of landing exactly how she wants, effectively removing the possibility of it ever being an unfavorable roll.

This is actually very much a thing touched upon in canon- If the Alpha Timeline predetermines what you’re going to have to do if you don’t want to die, is Free Will even a thing that exists? If you truly had an infinite amount of possibilities, and at any point, could take your life in a Drastically Different direction, then what does being ‘You’ mean, if ‘You’ can be two completely different people in two different Timelines? There’s no definitive answer to this, it’s a philosophical musing we’re left with, so. What do you think, Anon?