K8s and similar represent a current view on how systems should be designed and run from the ground up (largely based on the same observations you have made that the stateless workloads can be run with drastically less operational problems). If your architecture lines up with this approach (eg, following the 12-factor approach), there really are a lot of advantages. But no, legacy architected applications are just not going to benefit in the same way. I assume that there must be consultants and "thought leaders" out there who are pushing k8s and containerization as silver bullets and that's unfortunate.