I think he's responding to the fact that someone felt the need to create a new issue instead of attaching the information to the existing issue. It makes managing the work more difficult.
It's also worth noting that mfreed7 of Chromium (the person who initiated the proposal) is not the one who came up with the 357 number; that was zcorpan of Mozilla ( https://github.com/whatwg/html/issues/11523#issuecomment-320... ), so mfreed7 is talking about the list they got from zcorpan.