Maybe it wouldn’t have happened quite as fast as it did in Knives Out, but he still would’ve gotten to the bottom of things.
While Blanc is oblivious to that development, it’s worth mentioning he does some phenomenal detective work to figure out some key details behind Marta’s secret ahead of her official reveal.
He does enough that I believe it’s evident Blanc would’ve ultimately learned of Marta’s involvement even if she never revealed it.
A bulk of Knives Out shows Benoit Blanc is off the trail, as we learn early on that Harlan did kill himself in order to protect Marta, who was believed to have made a mistake with his medication.