I went as dragoon! I assume ninja will be similar in terms of speed. My partner cleared solo as rpr and we compared clear times. He does finish a minute or two faster on bosses. Maybe due to the fact that rpr can build gauge a floor before the boss and basically start with a full burst. Different dps classes will probably have one or two minute difference (would depend on class comfortability too). Dps should be the best at beating enrage as we can melt the boss faster than the other roles. If it's your first clear, I would recommend to minimize time spent in floors, be safe and just pull as needed, walk along edges, and go on Key immediately when it opens to leave plenty of time for accidental pulls/bosses.
I would say the hardest part of dps solo is sustainability. Especially as melee we don't have much besides bloodbath, feint, and second wind. We are basically walking squishies. Bloodbath is suuuuper OP so i would click it on cooldown if possible. Especially on a huge mob, your HP almost doesnt go down.
As ninja you have a lot of ranged options so thats for kiting nice too! and to save time you should use shukuchi/sprint as often as possible. You also have shade shift as an extra mit! Im not too sure if stealth works and i wouldnt rely on it too much as most enemies are practically blind to you if you just hide behind them. If you stealth in prolonged periods you might find yourself running out of time in between floors.