I didn't get that impression about Breath- mostly what I thought it was about was freedom/movement/dissolution. (Which I guess would make a Thief of Breath's power the ability to take freedom and movement away from others for their own gain, so probably super-speed combined with slowing things around them down? Still way less enabling of Vriska's issues than Light, though.) Sylph of Breath Aranea probably wouldn't have made the same egotistical mistake, either. Light really fed into what she did there- she got so caught up in how superficially great the "Fortune" part of her aspect is that she forgot that LUCK DO3SN'T R34LLY M4TT3R. Might still have tried something equally ill-advised, but it would have taken a very different form.
Re: Hope: Hope is canonically about belief, so it's entirely possible he could still have the voices of doom in his head and accidentally cause those things to become true because he believed they would. Re: Knight of Space powers: My guess would be extreme combat teleportation and ability to make temporary portals. (Fun fact: Knight of Space is the title I gave my sibling.)
Sollux hears the voices and worries about their prophecies so much that they become true? interesting. honestly both doom and life are really weird colours to match. both could probably work either way. thought sylph of life could play into jadeblood caste jobs, all the breeding cavern stuff. being knowledgeable about life would a rogue of doom use doom prophecies/voices to help others? rogue of life would be like condesce but better. using it to help others instead of herself, bestowing long life to those who want it, not who she wants to have it sylph of doom... knowledgeable about doom... im drawing a blank i'll make some more alt sprites for kan and nep, I do kinda like rogue of life, but sylph of life i think maybe works better? idfk
The Sylph thing is healing and fixing, so I think in game power terms a Sylph of Life would probably be really white-mage-y and able to fix problems with life (like injuries, including longstanding ones). Presumably a Rogue of Doom steals Doom to help others, so I think it'd be pretty likely we'd end up with a situation like Roxy with Void being a Green Lantern by stealing the nothingness- Rogue of Doom!Nepeta can steal her allies' Doom to make them harder to kill, and maybe redistribute it to enemies to screw them over. Sylph of Doom... maybe they can heal by bringing doom to things that are causing the problem? Like, all those cancer cells? They're doomed now. HIV infection? The virus is doomed. Poison? It's doomed.
hmm. interesting. good to know that sylph is fixing healing dealio, i thought it was just knowledgeable about aspect I like the ROgue of doom powers, but also sylph of doom.... I dont know which set works better! D:
Yeah, Sylph we know is healing from Aranea, both in her exposition and her actions. She can heal blindness (what she did to Terezi) and probably misfortune (which is why she thought she could heal the doomed timeline- again, she forgot LUCK DO3SN'T R34LLY M4TT3R)- I don't know if what she did to Jake to take down his mental blocks counts as healing metaphorical blindness, healing misfortune, or both, but either could potentially make sense.
might also "steal doom" in terms of aggro. Kite that fucking enemy nepeta. run them in circles while everyone else shots at the thing with abilities. You can do it kittycat.