You mentioned that Hollow Knight’s airdash on its own was sort of boring, just moving you in a straight line. Whats an interesting airdash?
Something with an arc of some kind, acceleration, deceleration, a hop, a glide.
In Guilty Gear, you have an airdash whose momentum carries you forward as you attack, allowing attacks to chain in ways they cannot off just a jump.
In Melty Blood and UNIEL you have an airdash that’s more like a hop forwards. Mario Odyssey’s dive could be considered an airdash too in this way, it even lifts you up slightly to let you just barely clear platforms.
The dash could start with momentum forwards that falls off as it progresses, and a resistance to gravity that also decreases as it progresses, so it travels straighter as it starts, then begins to fall like normal as it goes.
It could transition into a glide, or have glide-like physics should the player move it manually.
Ori and the Blind Forest’s bash is a really unique airdash-type move.
Morrigan’s airdash in Darkstalkers lets her tilt it up or down as she goes.
Celeste has an 8-way airdash that can transfer its momentum into the ground for a big boost, much like a wavedash, which is interesting.
There’s a lot of ways to toy with momentum and gravity. Hollow Knight’s movement options are all kind of simple and straightforward, only really becoming interesting when you have a bunch of them to combine. Hollow Knight’s double jump is out of the ordinary, being a bit like the jump of the DJC characters from Smash Bros (Yoshi, Peach, Mewtwo, Ness, etc), but this doesn’t increase its utility, it more exists to nerf its functionality versus airdashing and wall jumping, so it occupies a distinct niche relative to them (doesn’t have as fast startup, so it’s slower for climbing and moving laterally), which is fair, and helps make the sum of all of these moves more interesting to use, even if none of them are particularly interesting individually.
At least Hollow Knight doesn’t have the teleport from Axiom Verge. That teleport somehow manages to be even less interesting than HK’s airdash.