I don't know that I strictly agree that magic is real primarily for those who believe in it, but I do absolutely think whether people believe in it or not is a big part of the point.

Homestuck is really big on the importance of "ideas", and the key thing about magic is that the idea of magic clearly exists and is undeniable. So when Rose combines the idea of a wizard - even when that wizard is a statue and is, as such, a "fake" wizard - what do we expect to happen? Hussie talks about this a lot in the book commentary and I think it's such an interesting aspect of alchemy. Like, the idea that nothing you create is ever really new because you're creating ideas, which have always existed... as Scratch says, there is "nothing new in Paradox Space".