I agree with the suggestion when to use a server, but I think making it out to be an obvious physical law is a bit too far. Serveless runtimes can be massively multi-tenant, and in cases like Cloudflare have very little overhead per tenant, so they can share excess capacity for spikes, which you have to factor into your server. This gives them the ability to beat the server in thermodynamics. Maybe they will, maybe they won't but I don't think that's the argument that matters.