This is presently a 5 point line with the final point being available at level 15 and not at all worth the investment. I just used it in a match, all important towers were gone shortly after I hit level 10. If the game had lasted until I was level 15, there'd be nothing left to use uproot on except the citadel and even if there were important towers left, 100 dps(I'm assuming it applies the 100 damage on a per second basis) to surrounding units on a level 15 skill is completely lackluster. The 4th level of uproot barely had anything to do either and I doubt even it was worth the skill point.
There's also the issue that level for level, UB's spit can do more damage to buildings(UB shouldn't really be able to spit on buildings but whatever).
I would propose that uproot be changed to a 3 level skill line. Preferably one of the 2/5/8 lines. It's damage should go something like 700 at level 1, 1400 at level 2, and 2100 at level 3. The fact is, a skill that only affects enemy towers and then doesn't do a particularly outstanding job at it shouldn't be that large of a point investment. Ditch Violent Siege. Alternatively, keep move the bonus for violent siege to be a part of the normal uproot and have it scale with the normal uproot.