All of the comparisons with Poirot etc. are valid, especially considering the Agatha Christie influences on both Knives Out and (especially) Glass Onion, but actually the Golden Age detective Benoit Blanc most reminds me of is Lord Peter Wimsey. Especially with the epic obfuscating chattiness/stupidity. Blanc turns up his Southern Hokeyness to eleven when he wants people to underestimate him; Wimsey turns up his Upper-Class Twit, for the same reasons and in the same way. (And in both cases it’s a play on their own real mannerisms and accent, but they deploy it as a shield and a weapon.) Both are epically courteous, polite, and friendly, but you Do Not Want To Piss Them Off by being horrifying.
Also if anyone wants to write a backstory for Benoit/Philip in which Benoit saves Philip from a false accusation of murder and Philip spends years unsure whether he wants to get together with this man who saved him because gratitude is a terrifying burden, etc… omg I would read the fuck out of that. :D
Holy fuck you just had to add that last part and explode my whole entire brain didn’t you