There is a lot more to Starship than just full reusability, and "full reusability" encompasses a lot of variables too. How quick is turnaround? What sort of refurb is required? How many times is it reusable? For SS/SH construction is also cheap, the raptor is a really efficient engine, they will have high cadence given a lot of room for mass manufacturing efficiency gains, they're intended to be durable, and even the fuel is really cheap. Methalox is really economical to work with, and fuel definitely matters for a fully reusable design aimed at lowering costs as much as possible. RP-1 isn't cheap, and also has coking issues unlike methane.

Of course with Neutron not expected to launch, even under Rocket Lab's target, before 2024 they may have answers for a lot of this. I see nothing about fuel for example, maybe they've been working on their own great methalox design. But either way, F9 isn't going to be the comparison by the time they really get going.