"4" underperformed, but it also help secured her legacy. It is like the "4" era actually turned her into a bigger legend and icon.
Other R&B and pop acts with bigger hits have yet to even had an iconic moment, while the "4" era had her biggest. Yes, with better management, that era could have did more. However, it was a learning experience for her, and I am sure that she learned a great deal going forward. Obviously, Matthew didn't work, and she is also too big of a legend/icon to hire a "manager" especially since her brand is to be a powerful independent woman and mogul.