At which point you don't really need the flexibility of AWS and you might as well get a Dedicated Server elsewhere?

It'll still let you do the elastic scaling stuff, billing for actual usage instead of racked hardware.

Eric Brandwine (VP/DE @ AWS) said publicly in 2019 that EC2 had never scheduled different tenants on the same physical core at the same time, even before we learned about these kinds of side-channel attacks.

https://www.youtube.com/watch?v=kQ4H6XO-iao&t=2485s

Even before then, the sufficiently paranoid (but still bound to AWS for whatever reason) would track usage/steal/IO reporting along with best guesses for Amazon hardware expidenture and use that information to size instances to attempt to coincide with 1:1 node membership.

Yes (lowest vCPU seems to be 2 everywhere), and that protects against this attack. However, this thread was talking about airgapping hosts, which is needed for the general threat of VM escapes.

At least Fargate and Lightsail can select < 2 vCPU. (and maybe micro EC2 instance types?)

Well, that does sound like those were vulnerable then, if they happened to run on Zen 2. (Obviously microcode patched by now.)

As usual, cost is the biggest hindrance to security.