I often hear this argument that it is good for bursty load, but for real, there are a lot of inconvenient limitations. For exemple, you don't really control the number of concurrent instances or the scaling except if you pay for very expensive provisioning.

So you might have to wait for 10s or more to have a new lambda instance spawning up and replying to your requests. And you might have to have your function finish in 15 minutes, deals with the strange concurrency and scaling rules lambda is based on.