Even still, these explorers were able to harvest resources during their journey as well as immediately upon arrival at the destination.
With Mars, there’s nothing there. No fertile soil. No potable water. No known life. It’s an actively hostile environment. Colonizers to Mars will be exceptionally reliant on carrying the totality of their survival resources. Sure - if we spend the next centuries terraforming Mars robotically (or some other scheme), we could change the math on this - but I have a hard time swallowing the argument that crossing to, and colonizing, Mars is anything but orders of difficulty harder than the feats of those explorers. I’m a nerd and want to believe, but it’s fanatical thinking for… a long time.