In general, you wouldn't expect SPA or hybrid-SPA architectures to have scale coupling between the front-end and backend, because you'll be hitting specific API

In general, you wouldn't expect SPA or hybrid-SPA architectures to have scale coupling between the front-end and backend, because you'll be hitting specific APIs more aggressively than you'll be downloading the SPAs (even in a mixed-render environment). In addition, if your backend is serving multiple channels, then you've got another source of incoming requests, and it wouldn't be ideal to spinning up additional webservers when only the business logic tier needs to scale out. In general, the "one container per pod, usually" rule works pretty well. Adding more pods does create additional cognitive complexity, but by the time you need k8s, you really should have someone, or a team of someones, responsible for dealing with that -- I find that too often folks reach for Kubernetes when they could use a simpler container strategy (RIP, somewhat, Docker Swarm).