These cold start times are not hypothetical, as shown by multiple commenters in this thread. They also have been demonstrably impossible to optimize for years. Cold start times for .NET lambda functions are still an order of magnitude greater than that of Go (which also has a runtime). AOT compilation reduces the gap somewhat but even then the difference is noticeable enough on your monthly bill.

This dismissive “startup time doesn’t matter” outlook is why software written in C# and Java feels awful to use. PowerShell ISE was a laughingstock until Microsoft devoted thousands of man-hours over many years to make the experience less awful.