Distribution-first founders: how do you decide between fixing activation and adding reach? (I will not promote)

Context: B2B tool, week one after launch. 18 sign-ups, 7 completed setup, 5 used it, 1 came back. Traffic is back to baseline after the launch spike. My first-principles answer is "fix activation first": every new visitor today leaks at the same step, so reach just makes the leak bigger. The counter-argument I keep hearing is that 18 is too small a sample to optimise a funnel on, and you need volume before the data means anything. For those who've been here: which did you do first, and what number told you it was time to switch?