I've spoken to a half dozen YC founders this morning -- no one disagrees except the check size debt thing. Mostly "that is dumb" for that one.
For those who worked at startups when they were small (5–20 people), the difference between then and when they grew to be 100 or 200 people is night and day. Very real difference.
For those who haven't, think of class sizes. Do you think a uni class with 18 people in it will be the same as a survey with 200? Course not.
Three founders in my batch (early 2010s) have started companies in the past year and opted out of YC b/c of 1. batch size 2. YC doesn't mean to investors what it once did. The brand is heavily diluted.
YC is a broad based investment fund. The partners cannot handle the size of the batches or give the attention they once could. The partnership simply hasn't scaled.
Somewhat informed guess: partners don't want to give up their own returns by splitting it with more partners. Understandable -- human nature. But not good for YC as a whole.