Every platform comparison online treats this as a feature checklist. For a side hustle, the real question is different: how much traffic do you get before you have to generate it yourself, and how much of your margin does the platform keep for giving you that traffic?
Etsy: built-in traffic, built-in competition
Etsy sends you buyers who are already searching for handmade or niche goods, which is a real advantage for a side hustle with no marketing budget. The tradeoff is a crowded search results page and less control over your brand experience.
Shopify: full control, zero built-in traffic
A Shopify store is entirely yours, no marketplace fees eating your margin, but it also gets zero visitors until you send them there yourself, through ads, social, or an audience you already have.
Amazon: the biggest audience, the thinnest margins
Amazon's audience size is unmatched, but FBA fees, storage costs and the constant price pressure from competing listings mean a healthy top-line number can still leave a thin, or negative, margin if pricing wasn't planned from day one.
The realistic answer
Most successful side hustles start where the built-in traffic is (usually Etsy or Amazon, depending on the product), and only add a Shopify store once there is an existing audience worth directing to it.