Assuming the author's tests are single-thread, I'm pretty sure 1024 MB doesn't give you a full CPU core on Lambda. I could be wrong though; I haven't payed attention to Lambda in a long time. Last I remember it was 1.5 GB that gave you a full core. This alone makes the comparison between a mid-range server and Lambda unfair, not to mention the differences between language runtimes.
That said, if you are using Lambda and expecting to not pay extra you have somehow been mislead. Lambda is definitely more expensive per cycle than managing your own instances, and I doubt that will change any time soon.
Anyone using Lambda should _absolutely_ do load testing with different memory configurations. You will get different results, and should analyze what is best for your application.
When calculating the overall cost of managing your own instances you should also include time spent by your engineering team. There are particular tipping points in terms of overall requests per second at which point you'd save money by moving from Lambda to something like Fargate, and then even farther above that, you're better off using EC2. And then even above that, you should be running your own instances in a colo space. (And then at some point you should probably be building your own datacenters, and then at some point you should start colonizing the moon, and then... you get the idea.)
Are there any tools that allow you to load test Lambda services with different memory configurations?
When it comes to load testing tools I like Vegeta[1], personally. (Though I've also used some much more complicated proprietary tools when testing at great scale.)