Almost every k8s project I've looked at in the last few years is database bound. k8s is not really going to solve their scaling needs. They needed to plan more up front about what their application needed to look like in order to avoid that.
Yes, if your application looks like a web application that is cache friendly, k8s can really take you a long way.
In case it's not clear, nothing in my comment suggests that k8s will magically solve all your problems. It just provides abstractions that make growth (in size and complexity) of systems easier to manage, and helps to avoid lock-in to a single cloud vendor. The wider point is that thinking about architecture early will make scaling easier, and for most companies, k8s is likely to end up being a part of that.
The "web application" / cache-friendly part of your comment doesn't make much sense to me; k8s is pretty well agnostic to those kinds of details. You can orchestrate a database-bound system just as well as you can anything else, of course.
Yes, if your application looks like a web application that is cache friendly, k8s can really take you a long way.