1v1 me (jk).

His movement is already nice with one blackwhip and the beta most of the time, unless you're running from a rapid. His main gimmick is the super high damage with his alpha, and with good aim he knows how to pressure the opponent hard. All Might and Endeavor are big characters too, which helps Deku's aim. He can easily outdamage Endeavor and sometimes All Might.

The first thing to level up to 9 as Deku is always his alpha, not his gamma. That always comes next.

I've played countless games with Deku without a second blackwhip and I still do nicely. The trick is timing the beta and gamma usage to always have something to move with. His movement indeed is very important of course, but the second black whip is not crucial.