The article reads to me as pretty explicitly saying that the only real takeaway wrt k8s itself is "it was the wrong choice for us and then we compounded that wrong choice by making more wrong choices in how we implemented it."
Maybe I'm reading it with rose coloured glasses - but I feel like the only thing kubernetes "did wrong" is allowing them to host multiple control planes. Yes, you need 3+ CP instances for HA, but the expectation is you'd have 3 CP instances for X (say 10) workers for Y (say 100) apps. Their implied ratio was insane in comparison.
Since you can't run the Fargate control plane that indirectly solved that problem for them