There "cannot be two opinions?" Actually, there can be as many opinions as there are people (not just companies, but individual people) who have gone through the process. And they can reasonably vary, because not everyone and not every company needs YC or something like it, or can necessarily even benefit from it.

It's ridiculous to suggest that YC is a universally positive experience, just like it's ridiculous to suggest it's completely without value (based on the significant praise you refer to).