It's not just conservatism and liberalism that were tested in those two revolutions. It was France and Britain, their respective cultures, and all kinds of historical context that were at work. The revolutions didn't happen in an academic vacuum.

Conservatives do put a premium on social stability, which is why conservatives are explicit or implicit monarchists--oppressive monarchy being the most stable social order in history--and why they put up as many roadblocks as possible against breaking the power elite's hold over the populace.

In any case, I don't think progress is inevitable or "continual." The incremenatalist analogy you often hear from liberals is that progress happens in fits and starts, because it happens against the authoritarian wishes of the retrogressive conservatives who put up roadblocks at every turn, and because social progress also happens in opposition to our animal nature. We sabotage progress both individually and collectively.

I assume a natural context to all of this, so no, I don't presuppose any inevitability or guarantee that humanism will work out in the end. On the contrary, in the article I say, "To be sure, humanism, liberalism, modernism, and progressive artificiality may be tragic and doomed. We may think we’re progressing whereas we’re unknowingly engineering our downfall." And I expand on those hazards in various articles.

I don't have religious faith in nature or in the benefits of human creativity.