You know better than to use this example, I would hope... It's already been confirmed that Haki's effectiveness is reflected by the user's stamina (I also believe it's the case regarding DFs as well). Both Luffy and Doflamingo are at their worst here. All this would prove is C.790 Doflamingo is just a bit stronger than C.790 Luffy's Durability in terms of Haki.
Doflamingo vs BM Luffy being off-panel obviously means there's a lack of evidence for Doflamingo scaling since we don't see him actually hurt Luffy, but at the same time, he fought the dude for over 20 minutes and had him on the defense. It's strange to suggest any disparity between them when they were fighting seemingly on par until Luffy got the upper-hand.
Also, to be frank, Ace scarring WB is something I personally support, as I do think people relative to the Commanders/Admirals have the capability to harm a Yonko if they are giving it their all. The problem here is that we have scaling that puts people like Doffy <1/1000 Kaido or the same with Ace vs WB, when really, it's not anywhere near that massive.