Except we have the very big evidence that even during SNES era they lost a lot of exclusiviness and some even jumped ship to Genesis. So it isn't far fetched to imagine that Nintendo would still have lost majorly even with CD. Just look how much fuck they gave to third parties in N64, GC and Wii.
We keep pretending Nintendo sole mistake was to chose a format while Sega made a lot of mistakes and Sony was dumb luck, but that is being reducionist.
Nobody is saying that all these companies would continue making exclusive games for Nintendo.
What we are saying is that the games that were exclusive to PS1 and made the system likely would also be on N64 had Nintendo not gone the cartridge route. Even with sour relationships, they kept making SNES games (usually the superior port that sold better) so it's reasonable to say they would continue the next generation had Nintendo provided them a media that they could easily fit all the sound and audio these companies needed when entering the new 3d gaming world.
Even if Nintendo didn't dominate in America, it would likely have kept its lead and it would have dominated in Japan. Europe wasn't as big a market as it is now so even if PS1 won that area, I still firmly believe N64 would have been the worldwide market leader.