> Costs haven't fallen.

I disagree. I highly doubt reusing a booster has been more expensive to SpaceX than building new boosters. It is also speculated that at least the first few customers of reused boosters were given a discount.

If you are saying customer cost has not fallen, you may be correct. I would counter with the fact that SpaceX is already a low cost provider, lowering their price more may not increase their overall profits.

> The epoch-defining change would be back-to-back commercial launches with the same booster in a short period of time with zero or little retrofitting.

The booster SpaceX plans to reuse today is a "block 5" booster. This is basically the design that SpaceX hopes will enable that zero or little retrofitting reuse.