Cincinnati call centre is often dubbed as one of...shall we say not the best for DL. (Though my own experience with it has no great negatives.)

delta.com and their reservation system should not have let you ticket this, plain and simple. The MCT is not legal. Even if the flights were selected one-by-one in multi city, you should not be even presented an option where the connection time is below the MCT. But, it's a well known bug that sometimes DL will let you pick a 5 minute, 0 minute, sometimes even negative (yes, departure earlier than connecting flight arrival) MCT -- due to their primitive 1980's era reservations system that is not by itself aware of the concept of time I believe, and the flights have to be manually arranged in the right order. (That is also why your ticket, and delta.com, will often have the wrong departure/arrival time for non-DL flights, as upon schedule changes it sometimes never gets updated, not even months after the change. So for any non-DL flights, always check the operating carrier's web site for the real departure time, don't trust DL. Just a side note. I've had it happen where a non-DL flight changed from 11am to 4pm departure, making me miss my connection by some 3.5 hours. But, on delta.com and on the DL ticket all was showing peachy and no problem. It took a lot of convincing to have the DL agents look at the real flight schedules and not the garbage that their reservations system shows before they would change it. And in that particular case they did change it just by changing flights, 'revalidating' the ticket, but not actually repricing it, so that is where my advice comes from BTW.)

Here DL has you ticketed from origin to destination (CDG), and as the MCT is not valid it is their responsibility to change it/fix it, and as the price was agreed upon by the parties at purchase, the price should not change. It certainly is possible, but these days it needs a few levels of escalation and approval. From my past experience, first the phone rep's supervisor needs to sign off on it, then go to their manager, who also has to sign off, and then the manager has to seek approval, and only if it's granted then such a pricing override can be done. I do think there is also a quicker way to do it: simply change flights and reticket without repricing (so your fare calculation will still show the old flights, the ticket and flights will be updated, but the fare calculation will stay the same), though that is a workaround that I believe is "not supposed to be used," and may be not all agents have access to it.

Really here you need to get a hold of someone at IXXRES or IRRRES. Only these two reservations agent groups have any sort of real access, knowledge or understanding of how things work...but, even most agents inside DL don't know how to directly reach either of these two groups (or at least so they claim).