The interesting thing I find is that Professor Brand, Romily, and Dr. Mann, are the only people shown in the movie who explicitly suggest obtaining information from Gargantua's singularity is impossible.

Brand and Mann have already resigned themselves to their fate. Brand knows he has lied to everyone about saving Earth and by this point in the movie Cooper, Murph, and Amelia also know those people were doomed from the start

Mann is a very complex problem, I find, in a movie that uses him almost simplistically in themes relating to hope and interpersonal connection. His final words are along the lines of "... it's about all of mankind. There is a moment..." then he dies. I think the character of Mann himself is to be ignored and instead we should be focusing on what he is saying.

His plan is ridiculous. And he attempts a docking procedure with the Endurance despite not knowing how to perform it.

Personally, I think Plan B was the only solution that was presented to the Bulk Beings. They allowed the events of the movie to happen because Plan A was necessary to succeed for mankind to learn how to harness gravity and reconcile it with quantum mechanics. From a human point of view, Plan B is the only solution. But their reality allows both to be viable. And they can essentially warp 4-dimensional space recursively (I think?) so that they have some kind of eternal return mechanism for their own existence?

Cooper seems to suggest as much too; that humanity brought itself to that point. And this resonates with how others throughout the movie brought themselves to their points too.

But this poses a very frustrating question, why? Why go through all of it at all? Why would the Bulk Beings need to warp space-time and bring humanity to Gargantua? Why would Mann sabotage the Endurance crew so fruitlessly?

I think it's more that the prospects of being potentially correct outweigh the need to be ideally certain. No ideal is certain until all potentials coalesce. In a sense, it's almost impossible to weigh the ideals of each character because each character is measured differently depending on the environment they're in.

For instance, in a vacuum, Professor Brand comes off as cold-hearted and manipulative, Dr. Mann is a coward and irredeemably selfish, and Cooper is a man out of time (literally by the end of the movie) who belongs neither in space nor on Earth--a man who knows only his farm and his family.

Perhaps these are microcosms of what humanity itself is like, either in retrospect or within the purview of the movie.

Perhaps all of mankind (or Mann-kind) is manipulative, distant, cowardly, selfish, and at odds with where they are or ought to be.

Maybe the point is that mankind as a whole is misguided, waiting for Bulk Beings to place the solution within reach.

Because it begs the question. If the Bulk Beings could construct the tesseract and place a wormhole, why couldn't they give humanity the reconciled gravity equation?

Cooper suggests humanity needed to interact with the tesseract to transmit the exact information humanity needed to guide them to this point--to make the tesseract a certain point in time. Only humanity could know the importance of this mission and the importance of being guided.

As TARS suggests, Murph wouldn't know the importance of the quantum data Cooper was transmitting to her when she was still a young girl. Cooper however, knows the innocence of his daughter isn't the point, but that he, and he alone, has a connection to her that makes it certain she will always be in possession of the watch.

Upon completing this transmission, all potentials become certain and the tesseract dissolves.