The fossil record for cephalopods is actually pretty strong because most of them millions of years ago belonged to families that had hard shells, like the nautilus of today. They're some of the cheapest fossils you can get your hands on due to how common they are. They ruled the seas for a very long time as the most abundant form of complex life in their habitat.
Close relatives of modern squid and octopus which took over after the fall of the hard shelled families are much less common since in many, the only thing to fossilize is the beak (though some like cuttlefish have hard "inner" shells). That being said I'm pretty sure we do have ancient beaks that scale to creatures that would have been larger than even the colossal/giant squids of today.
I know you don't have much respect for them but everything I've just summarized would be extremely surface level for a real evolutionary biologist. The evolution of cephalopods is interesting considering their physiology differs so much from ours, but I don't assign credit to aliens for their existence any more than I would a snail or slug.