“the development from the first drawing to the last is just startling”

Well, to put it in perspective: before I did that first panel, the only time I had ever even tried to draw a superhero comic book was a six-page opus called [I think] Karate Master vs. Plant Man. So I was a rank beginner at this style with nowhere to go but up. I expect to never experience such a pronounced artistic growth spurt as this, ever again.