I think there is still a residual bias in the scientific community toward the Neanderthals. For a long time, they were viewed as a less intelligent brutish humanoid. This bias has slipped into our language when we call a person a neanderthal. It's only in the past few decades that our understanding of Neanderthals is changing.
I have no issue with our ancestors having sex with Neanderthals. It's better than thinking that our ancestors totally obliterated them in the first genocidal campaign in human history, or accepting the belief that the two species operated in a vacuum and never met the other.
Returning to the topic, I think many of the diagrams that proponents of ancient alien visitation cited as evidence were rather the creation of an imaginative, intelligent artist. Our ancestors were capable of creating fantasy and science fiction. During the Roman Empire, Lucian created stories, in True History, wherein humans travel to the Moon and to Venus, of the existence of extraterrestrial life, and of wars between planets. I think it's conceivable that he wasn't the only writer who wrote on these matters in the ancient world.
Like I said earlier, this inability to envision our ancestors as like us was a bias - a terrible bias at that - that I would like to see buried along with the other beliefs like that blacks were less intelligent and less brave than whites, or that a woman's place was in the house and that such an individual didn't have an intelligent mind and was incapable of uttering an opinion.
I don't know what aliens will look like, but I would like to think they feel emotions, they form family and friendship bonds, they go to bed at night and wake up in the morning to go to work, they like to eat and to drink, they like to party, and they like music and dancing. This is my bias. I can't imagine an alien civilization that doesn't embrace some of these likes. This is my human weakness - that I like to think at some fundamental level they are like us.