The only phrase which really is "too French" here is "proposes to the sagacity of its admirers". (It's not wrong, but not many English speakers still use "propose" in its sense of "set before someone as a goal".) Other than that, I see a well-balanced sentence in which every word has a purpose – but "well-balanced" versus "straight-forward" is a matter of taste.
Every time I read that sentence I can't help but picture some huckster standing on a soap box at an intersection in an impoverished neighborhood in the 30s. It's so clearly crafted to impress rather than inform that I can't help but feel a sales pitch is coming.
Well, yeah, which just goes to show that you're interpreting a work written by a French alchemist in 1929 in an American cultural context where everything is some kind of sales pitch - which is why you're getting the wrong end of the stick.
I agree that's the most cumbersome phrase. But I think the difficulty people are perceiving here is more in the grammar being difficult to parse rather than in the vocabulary being florid.
