I saw them hiring Rust devs recently, which makes me feel like they do things efficiently(hopefully). That being said, Serverless is the greed-driven-model, where you start by thinking, "meh, we don't need that many queries/executions/whatever anyways, we will save plenty mulas we'd waste otherwise renting a reserved instance sitting idle most of the time", then something bad happens and you overrun the bill and then go into "sh+t, need to always rent that higher tier, else we risk going bankrupt" and since your stuff is already built, you can no longer change your stuff without another big re-write and fear or breaking things.