This sort of pricing isn’t unusual even for no-name brands.
Yes, you can get arguably nicer tailored cotton trousers at this price point. You will probably end up paying significantly more getting similar pleated trousers made by a decent tailor though.
Better off the peg? I don’t know, these are a fairly unique product, With a quick look Google isn’t finding any particularly similar products at any price point.
I have some friends in this space, even with margins like this it’s not an easy business to survive in. Those that do are generally doing something special, unless they’re really big names which Issey Miyake isn’t.
Point is they're not 500-quality trousers, that's well into tailored cotton territory for a start, or you could buy better off the peg for much less.