Dungeons & Dragons 5.1E — Monk

[Sorinth]

I'd be wary of Step of the Wind as written because you can easily get a BA Dash and so you can get truly absurd movement.

Although I do tend to agree that Mobile is kind of a feat tax, many subclasses have ways of handling it so I think a better solution might be to follow the Fighter's ASI progression. That way you can grab mobile easily if you want it, but the subclass features that already grant something similar mean that they can spend those ASI.

I like Abundant Step, but given that Monks have slow fall (I think you have them keeping their abilities that weren't listed) I wouldn't even bother with the gently float to the ground. If through whatever shenanigans they get super high in the air and slow fall can't cover the fall damage so be it.

Decisive Strike is a copy of Kensei's Unerring Accuracy so I would probably try for something else.

My last comment is that because of the change in Ki (more at early levels, less at high levels) you might want to readjust the ki for Empty Body. Spending 8 ki when you had 18 to use Astral Projection is one thing, spending 8 ki when you have 11 ki is something else entirely. Even the 4 ki to transform is a much bigger cost then it was before. Similarly ki hungry subclasses have been unintentionally(?) hurt by this ki change and would potentially need to be adjusted.