Stopped him from touring solo, for one. Held too many of his songs off their albums, for another. Brian was shot, and they needed a new musical leader. Dennis was the only once close to capable because Carl just didn't write enough stuff. Dennis was the best writer they had. He should have quit and went solo after Surf's Up.
Well stopping him touring solo happened that very year didn't it? So obviously wasn't long standing issue.
And Dennis was the one who took his songs off Surf's Up. He also had the opportunity to sing the lead on their big attempt at a hit single from the Holland album but decided to surf instead. It would have stood a much better chance of being a hit if it had had a recognizable Beach Boy singing it and he would have had something to perform in concert every night.
As he had the space for between 2 to 4 songs on every album from Friends to Holland I don't think it's fair to say the group were holding him back then. He absolutely should have been involved after Holland and they should have been using a combination of his songs and Brian's songs. If they had though there would have been no POB...