They didn't make bold claims though (at least in a way that we humans can understand).

However, "c will never be able to be passed" is a very bold claim. IMO we can leave room for exploration by saying "c can't be passed with our current model of physics due to relativity, in the context of what we refer to as spacetime", which would still be correct, yet leave the door open for any future discoveries.

We do laughat alchemists and astrologists though. We don't know what Australopithecus thoyght they knew.

That's my point, when we pass those barriers it won't be "us" anymore. It won't be like looking back at essentially a dumber version of ourselves, but like a distinct species.