Steve is bloodlusted here so he's not going to try hit-and-run tactics

he's just going to try and kill bro.
Which, bringing back to that point, Steve is going to have a difficult time even hitting Yu with blows or directly getting him in the path of lava, since Yu will know how durable he is off-rip with analysis, he'll immediately just lead with blitzing via Monster Stance and from there he can kinda just zoom around Steve.
He can't place it directly on top of Yu without placing the lava against a block. He can place it directly next to him, but it'll still be at a distance from Yu before it starts to spread. All Yu needs to do in that situation is back-step and then swerve.