Trying to tell someone their baby is ugly. Not literally of course. But early on as a manager, I had to have a tough conversation with the team who built our product that because of the accrued tech debt, anything we ever wanted to do would be hampered or just impossible to do. The market was moving quickly, competitors were able to build and deploy new features 2-3 times faster than us, and with a org as complex as our was, it felt like cramming square blocks into triangular holes. I just got fed up. Sometimes you have to rip the bandaid off and show people that the way things are will lead to their demise. This isn't the most ideal strategy, but if people are being stubborn and refuse to see the truth, you have to make them feel it somehow. Especially if the blame is going to inevitably fall on you. Once we got a new system up and customers gave great reviews, it was much easier to get buy-in and my street cred shot through the roof. I'd say come to the table with data, a plan, and poke holes in what already exists. If that doesn't work, step back and let the cards fall where they may.