Ball was playing close to (but not quite) career best footy towards the end of 2010 and in 2011. His issues toward the end of his career stemmed from the knee reco and back injuries, the latter which finished him off completely.
Karnezis would likely have failed at Collingwood even if he didn't have OP in hindsight. It's certainly not the primary reason for his failure to establish himself as an AFL player.
Balls career was impacted by OP the same way Judd's was. Temporarily.
It wouldn't have impacted their decision at all.
I think it's been generally considered as a fact (in the football community) that Luke Ball lost a lot of speed and agility after his OP, his kicking penetration also went to shit even before his ACL and back injuries.. All those things are common for someone who had OP, which results in the groin becoming tight and inflamed.
There was something wrong with Karnezis, everyone could see he had the talent to become an AFL player but there was something holding him back. It's not out of the question OP played a role in that and hurt his physical output... We'll probably never know though.
If I was the GWS list management team and I had to decide which players to keep and which to trade, on going medical conditions would play a big factor in that decision. Major injuries can also be a big catalyst for players deciding to change clubs.
Treating OP has improved in recent times so hopefully the surgery has cleaned a lot of things up because we really need Treloar to reach an All Australian level if we're to make an impact in the finals in the next few years, the kid could easily reach top 5 midfielders in the game if his body lets him.