Today's P/peak-book is 1.65 ($497.50/$301), and so there's definitely a chance of not hitting inflation + 6.5% over the next seven years.
Right?

If that guy said so, then it must be so : )
The historical record is of course stuffed to the gills with a huge stretch of gradually falling valuation levels, so those odds based on observation do express that headwind. They *might* be a bit pessimistic? Beats me.

My more recent post was more constructed along these basic lines: As long as the value growth over the long haul is higher than your hurdle rate, you'll eventually manage your hurdle rate even if you pay a richer-than-usual price.

Imagine today's valuation is 20% above the future average but you're nimble enough to manage an exit at a valuation multiple only 10% lower than today's purchase. If share value grows at (say) inflation + 7.5%/year, and you pay 10% more than your future exit multiple, then you'll still get inflation + 6.5% if you wait a decade.

Jim