This suggests that he see the limiting factor for AI to be hardware, however I've heard people argue that we probably already have the hardware needed for human-level AI if we get the software right

We do, but it's not cost effective or fast enough - so humans are cheaper and (sometimes) better. Within a decade, the estimated hardware may cost around 100 USD and the performance difference won't be there. Sometime around then, things seem likely to get more interesting.