It may not be as simple as just moving him up- they may not have the space to move him into the next room or there may be other kids who need to move up first. Or they may believe he's not emotionally/developmentally ready to move up ahead of time.
It actually sounds like they ARE doing what they can to keep him entertained. Honestly (not you OP) the CC worker bashing on BH drives me batty
Oh and the dummy thing may be a policy in the next room up- in the centre my kids are at, comfort items are strongly discouraged apart from at rest time from the toddler room up. So that may be what the comment was about.
I don't think there's much you can do at home except try not to worry- it seems like it's just a situational issue and not to do with his personality/temperament.
My DS was one of the biggest in his room and just stomped all over the babies and as a February baby there was no way they could move him up in term 4, they just did what yours seem to be doing, which was just try to protect the babies (lol) and send him out to the big kids whenever possible.