I don't want to take away from the appreciation of this awesome technical achievement, but in practice I have noticed that:

- Cold starts are kinda rare, sure it sucks that your request takes 600ms, but that means you are the first user. If you would've been served by a container that was just scaled up, you'd have been waiting for much longer

- Microservices and AWS lambda are inherently stateless, and do a ton of things to make themselves useful - get credentials, establish db connections, query configuration endpoints, all of which take time, usually more than your runtime spends booting up.

As much as I like lambdas for their deployment and operational simplicity, if you want the best UX, they have inherent technical limitations which make them the wrong choice.