Long time lurker, first time poster.
Just piping up to say, I'm struggling to see how you could come to some of those conclusions having watched a replay. Don't take this the wrong way, I'm not trying to troll you but I am baffled as to how you could see it that way. Pictorial evidence to follow.
1 - He doesn't join the ruck correctly. He comes from the side. Just because he comes from the in-goal area originally doesn't mean he can come in on an angle.
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Here he is about to engage.
Here he is with a foot over the line still not bound (based on the his body position and the guys on the ground, he can't have a shoulder on a player in the ruck there) with a hand on TKB shoving him off the ball.
2 - Joubert doesn't accept his entry is legal.
Here is Joubert signaling advantage to the Chiefs.
3 - Messam enters the ruck from the Chiefs side.
Here is Messam (middle of the screen, red & white boots) bound to the ruck and driving him back. Note even at this point Messam's feet are behind the hindmost Chiefs foot, so I'm not sure how you could possibly conclude he came in from the Brumbies side.
The only vaguely controversial thing that Messam did was continue the clearout into the in-goal. As the ruck technically ends at the goal line perhaps you could say he should stop driving once Powers is behind the line. But that's a pretty minor point I'd say. As it happens Powers ends up falling over the pile of bodies so it's not like Messam drove him miles back or anything.