Unless someone can convince me otherwise I'm not playing against oak unless it's a player below 35% or so.  There is no counter to his lame minion build that I've found.  He just throws up a few flags, collects spirits, and rapes your base.  The last game against a minion oak we were actively trying to prevent it from around level 4-5.  I upped tower offense and defense, we tried to kill creeps away from his flags ... it didn't matter.  Despite dominating the game otherwise our citadel fell to his spirits.  We had both of their portals and they'd never taken one of ours.  For the last half of the game our TB sat on our citadel trying to kill them as they came.

Another game I was oculus and I upped our building D and O almost to max and sat at the citadel using chain lightning and blast off to kill them.  The best I could do was freeze our citadel hp at around 15k and I had to stay there the rest of the game, effectively taking me out of the fight.

If Oculus can't prevent it I don't see how it's possible.  It's well past time Stardock fixed Oak's many ridiculous OP traits.

This wasn't a problem until recently because most people didn't realize it was possible.  Now everyone sees it and is imitating it. It's getting out of hand.