I did some numbers on Bula pre and post injury in the deep dive thread and there is a significant drop off in perfomance on both sides of the pill (
go here to dig into the detail). The issue is that the contract was signed while he was out injured so while it is highly likely it is the injury causing the issues the contract saga can't be thrown out the window. I am giving him the benefit of the doubt; but now the season is cooked we probably should have him and AD scheduled for early surgery.
In relation to the kick in the first couple of minutes I doubt any fullback would have been able to tell from where he was postioned if O'Sullivan was behind or in front of the 40. He would be relying on others to relay the information. I think if you watch the replay Bulla looks to be saying (to Skelton I think) something like you said he was out. Having said that he was caught well infield so his positioning was not great.
My gut feel is that both AD and Bula are (subconsciously) trying to protect their shoulders so are not taking on the man in the collision and are trying to go around them - pushing the attack sideways and making them easy targets. Given neither had a great passing game to start with playing with a damaged shoulder limits the passing game further and makes it difficult for those outside.
Given their importance to the team I think that if I was Benji I would have probably made a similar call in playing them to keep the season alive. Now that opportunity has all but passed there is no need to flog the dead horses; get em fixed and focus on assessing and developing players for 2027.