At the very least, even if you argue that Luffy and Gaban were discussing demonic presence with Imu's Haki(which isn't based on anything canon, tbh), that would still be including the fact that Luffy ran in to the five of them last arc, and they also either have the demonic presence or don't, which obviously makes Imcel different. His DF also doesn't work like the others, and he doesn't seem to have the conventional Regen.
Saturn fought Luffy....at least kinda? But sure, the others will get more showings later on. I find it hard to imagine the future Sanji and Law victims will end up doing something better than low diffing Luffy tho...