In my opinion, Thanos is sort of like dexter. Being born in blood and all. Except he kills innocents too of course lol.
I think if you scrape away the obvious differences, such as Thanos being a mutant born on Titan with enhanced strength and other physicals and the purple skin, there is still very little similarities between the two. Thanos's hatred and disregard for human life grew gradually as he grew up, compared to Dexter's which occurred when he witnessed what happened in the containment unit. Admittedly in the Thanos Rising storyline his mother tries to kill him however no violence actually occurred. There is also the fact that to everyone else Dexter is just a normal guy, he hides the killer inside of him, which is the complete opposite of Thanos, who also does so on a much grander scale.
Honestly aside from the fact that they're both killers with screwed up childhoods they have next to nothing in common. Dexter has more in common with the Punisher actually, they both work/worked in law enforcement, they both kill bad people exclusively, and they both believe what they're doing is inherently bad but they can't stop because they're psychotic.
" the book is beginning to feel like Dexter in Space"
Called it, like a month ago :P
No. I can't imagine how limited your scope must be for you to think Thanos is more like Dexter after Thanos Rising.