the change to iron boots that removed wavedashing was that it no longer gives you double the speed you had before, but just the speed you had before, unfortunately this change made the velocity you have after iron bootsing very inconsistent, mostly because it's not working as intended. depending on the frame you could lose almost no momentum, to almost all of it. i assume it all comes down to how much the physics engine had to reduce your velocity during the collision that happens on the frame iron boots activate.