IMO I think the Float out of nowhere is kinda bullshit. I felt the same thing about Blackwhip, in terms of Deku awakening it, losing control, and then using it again relatively proficiently within the same arc.
I guess Horikoshi can always do the flashback meme of how/why Deku is able to do it, everyone saw this coming a mile away so I guess Horikoshi felt like it'd be boring to introduce it beforehand?
I'd thought Deku would 'meet' each personality as he awakened them like he did Blackwhip.
Plus is there no kickback to utilizing three quirks at the same time? He struggled just to use Blackwhip previously.