I can see this being a pain. 4 tower spamming Rooks with speed items have the potential to dominate. They can each grab a lane and block it with towers. If any one of them is being attacked by more than 1 DG, the others have plenty of time to come to their allies aid and spam even more towers.
However, this is part of a much larger problem and that problem is DG stacking. Played a 2v2 game against 2 spit/grasp specced UBs in Prison. They always traveled together with speed items and Spit/Grasp/Grasp/Spit in that order. Even if you ran, the spit would kill you and there is no amount of healing or absorption that will save you from it. And considering Prison has no lanes, they controlled the center of the map until their war score and gold was way higher than ours and proceeded to win.
In another game there was a 3v3 where one team would quickly change all of their DGs to Regulus right before the host hit the start button. Some of us quickly cancelled the ready button when we saw this and called them out on it. They said they were not gonna do it anymore but proceeded to quickly switch their DGs back to Regulus and, again, I cancelled my ready button. After a few back and forths on this, I left the lobby.
DG stacking is going to be one of the major balance issues of this game in the future. Its already gaining traction.
Other than completely reworking the abilities, the two simples solutions to this are:
1. Limit the number of times a DG can be picked, depending on map size.
or
2. Lower the effectiveness of similar stacking abilities when combined. For example, if two UBs spit on you, the second spit deals reduced damage. If you get Penitenced, by Oak, any subsequent Penitences from other Oaks will deal less damage for the duration of Penitence's cool down. This makes it so that it never affects a single Oak but 2 Oaks will see a reduced output. Note: these are just examples and I don't think UB or Oak is OP.