The last flood in 1974 reached higher levels in Brisbane, but I haven't seen anything explaining to what extent (if any) the flood levels were lower this time because of the dam? Would it have been even worse without the dam?
At the very least it let them control the flow a little bit so we didn't just get hit by a massive wave all in one go.
I think the general consensus is that the flooding would have been worse than 1974 had the dam not mitigated what it did. Investigations and modelling will determine to what extent the releases from the dam increased the flood level.
I expect the outcome will be a new operating manual for the Dam, and more frequent minor flooding in keeping with an aggressive plan of keeping the dam at 100% (water storage) level, leaving the extra 100% of flood mitigation level free as soon as possible.
Another possible outcome may be more dams on some of the other river systems, such as the Bremer river.
At the very least it let them control the flow a little bit so we didn't just get hit by a massive wave all in one go.