Two thoughts.

A $20/month Gemini subscription is truly all you need, then yeah, sure.... obviously a homelab setup is a ridiculous alternative on a pure cost basis. For most people doing "real" work with LLMs 40+ hours per week, a more apt comparison would be one or multiple $200/month subscriptions. At which point the break-even point of a homelab is much sooner.

However, most people running homelabs are doing it for other reasons. Independence, learning, and/or privacy issues.