Yes, YC is a good deal in an alternative reality where YC is the only choice. However, I talked about doing YC in the real world, where other alternatives exist.
I think you are missing my assumption in my OP "in the early stage of a startup". In fact at that stage of startup, even if you have a better deal than YC, you might still want to do YC (so you would take both two deals) because even after your take the better deal, YC can still gives your startup >6.4% growth.