The entire YC team can advise ~66 startups and they have ~14 people which suggests a person can advise 4-5 startups at a YC-level. It's not quite equivalent since YC has the benefit of multiple perspectives though at the cost of increased coordination.
The truth of b & c are completely dependent on who hmexx is.
YC also has Yuri Milner, Andreessen Horowitz, General Catalyst, and Maverick Capital working with any company which takes a convertible note.
Furthermore, those companies taking the note have a much longer runway than hmexx will provide and will be plugged in to a network of later stage investors.
Finally, each YC company has access to the other companies in its class and the YC alumni...and lots of other things in the valley.
It's logically possible hmexx could approach a similar level of success but it looks unlikely.
YC has those things now. At the beginning it didn't have any of these things, and a few really successful startups emerged from those early days even with YC not having guaranteed follow on funding, not having a large network of alumni and not having the reputation.
The truth of b & c are completely dependent on who hmexx is.