Startup valuations are not accurate. Your comment essentially proves the point: If an investor is going to fund a company at valuation X, they prefer that X is a combination of cash and stock and not purely stock. This implies that a dollar of valued startup is not worth a dollar, which should be an axiom.

A 3 MM dollar company comprised of 2 MM stock and 1 MM cash is more desirable than one with just 3MM in stock.