[Touc]

and a speed decrease of summons across the board is already planned (just not implemented yet)

it's been live for days (@ mandrakes / vine summons)

Has it? Then I think you need to decrease the speed of summons again. I never noticed any difference at all.

Even if the summons were walking-speed, they would still be good just out of virtue of being obstacles that the summoner can't trip over.

This shouldn't be hard to imagine for people who have fought in Osrona's arena before (those damn lampposts) or the central tournament arena - think of an RPB box that's got a few props in it that you get dead-stopped on if you accidentally step near them, requiring you to carefully extricate yourself to avoid being stuck. Then imagine that your enemy can just walk over them without penalty while you get stuck on them.

RPBs are all about movement (unless you're fighting an autohit build). If your movement is interrupted and becomes telegraphed, you're dead. Vines and mandrakes disrupt that movement and disrupt that flow. It's part of why Ent summons were extremely good. They should be passable for enemies, but do damage for passing over them instead, so you have to make the conscious choice of either going around or pushing through the hedge to attack the summoner.