No he got the smartest advice. People that really think this was a dumb move by Ngannou don't really see the big picture. They probably only watch UFC as well. Ngannou is looking to cross over and do both. That exposure to 2 completely different fan bases. UFC doesn't do a good job promoting fighters, the biggest stars promoted themselves. UFC thought Diaz bros weren't needle movers and no one cared to watch them fight. They just needed exposure and the Conor fight brought that and Nate became a star after that.
UFC had Nate Diaz under contract for a long time and couldn't promote him and had him on a low fight purse contract. After the Conor fight Diaz made the best of the situation and promoted himself and stood his ground and got a better contract. Nate Diaz was one of UFC's biggest stars but UFC never promoted him prior to the Conor rematches. They didn't understand Nate's worth/value and were surprised that he was gaining a lot of casual fans.
You bring up Wilder's last PPV numbers but he still got paid 10 million. Wilder is an 8 figure fighter - just like many other boxers. Ngannou will do just fine even as the B-Side. Boxing PPV numbers aren't super high and they still get paid more than UFC fighters. Lots of fights are also not on PPV and they still get paid millions per fight. UFC stacks their cards, boxing it's really about the main event only. Even if UFC sells high numbers, the fighters aren't getting that cut, so there's no real reason to bring up PPV numbers anyways. Only champions get a cut and it's small percentage compared to how they do the splits in boxing.
It's apparently not that much exposure to a different fan base, based on the numbers from Wilder's last fight. They only have estimates from his last fight, but it looks like he got paid more than the entire event brought in after badly missing estimates and the promoters just ate a huge loss, and his opponent didn't make that much.
I doubt he'd make more, certainly not much more, boxing Wilder than he would have made fighting Jones in the UFC, where he gets PPV points and would certainly sell more PPVs, and that is IF the Wilder fight even happens. It would also be basically another year away from MMA. If he takes a year away and gets KO'd by Wilder for $2 million, then that is a loss compared to having stayed in the UFC and defended his title.
They did understand Nate's worth/value before the Conor fights, which wasn't anything special before he beat Conor. If he'd never fought Conor, or had lost their first fight, nobody would have paid much attention to him after. They have like 700 fighters on the roster, so they promote the events and the fighters, do the countdown shows etc, but of course the fighters have to set themselves apart from the rest, and Nate couldn't have without beating Conor.
This was Wilder's disclosed purse from his title defense before Fury took his belt in their rematch, against a 31-1 former interim champ whose only loss was against Wilder for the title the year before.