Let’s not forget that PG's full-time job is YC whereas Drew's full-time job is as Dropbox CEO. I think the difference is already apparent in that sentence – Drew isn’t a substitute for PG and PG isn’t a substitute for Drew.

YC has never been just PG, there has always been a group of partners (which has increased over a period of time and includes some part-time founders) and you can always arrange time with the partners during office hours.

Sure PG and the other partners can provide you with some excellent advice but, no one is an expert in every single vertical. YC fully understand that which is why they bring experts in during YC for dinners as well as hosting conferences for the founders throughout the year.

I believe the alumni network has made YC stronger because, they've funded so many companies that there's likely to be other members in the alumni network within the same industry and/or using a similar technology to you – and if you ever need their help then they are there to help you.