Or in non-anthropic terms, strong AI could be done on present-day hardware, if we only knew how, and our survival so far is down to blind luck in not yet discovering the right ideas?

For how long, in your estimate, has the hardware been powerful enough for this to be so?

If Eurisko was a non-zero step towards strong AI, would it have been any bigger a step if Lenat had been using present-day hardware? Or did it fizzle because it didn't have sufficiently rich self-improvement capabilities, regardless of how fast it might have been implemented?