Engagement matters most. Engagement is actually a function of great product and great distribution. Engagement is thought-of mostly as a product issue but in many cases, it also expresses itself as a distribution problem particularly where there is no possibility for a "single player" experience (marketplaces, feedback loops, anything attempting to be inherently social)

If you have sustained engagement (a product experience loved by users) you will be successful, limited only by the potential number of people in the world that need the experience you provide and growing at a rate closely correlated to your distribution channels.

Inefficient distribution is easier to optimize for then insufficient product. So to this extent, product matters more. But available distribution channels (or more accurately, the unavailable distribution tactics) also can define a company's fundraising options, and more definitively, the overall cultural and corporate DNA of the organization that forms around product & distribution.

This is the best, most generalized answer I can provide to your question. Happy to talk to you and provide you a more contextually relevant answer to your own circumstances.