Curunauth: Most builds focusing on soaring demon use the leaping finisher to get huge single hits. However, the machine-gun crossbow is certainly a fun benefit to soaring builds, and the silver and gold phases of my low-level Demon run ( https://www.gog.com/forum/sacred_series/lowlevel_run_stuck_in_niobium_at_level_18 ) definitely took advantage of this fighter-jet mode (I guess hovering out of reach over water makes it more of an attack helicopter . . . ).

High mobility plus a high-fire-rate bow is definitely a useful general strategy for full play-throughs at least up through Niobium - being able to outmaneuver enemies and pile on the damage in between moves (or after kiting them to an obstacle) completely breaks a lot of encounters (but will make you truly hate enclosed spaces and enemies that can root you in place). My fast-firing wood elf is quite lethal and fairly safe when mounted, even though she's L55 in Niobium, fighting enemies well above her level; the DPS multiplier on a flying demon is even better (but I can't speak to actual viability in Niobium as mine is a stupid challenge run and currently stalled).

I'd be interested in hearing if you did come up with a build that worked well in Platinum or higher!