Probably really dumb, but Geist with Ult?
I assume the small boost to speed at the cost of stamina would allow it to get another chance to equalize, gaining speed from its opponent, reverting Ult to its original state, and repeating once it runs low again.
Also, how durable is the LR string launcher?
If I use it properly (i.e not clicking it) will it break, and after how long?

Well the rubber adds to much friction so there's really no way for geist to spin steal efficiently. That's why things like bearing and low friction materials are constantly in the meta.