Docker-compose isn't going to help you with Let's Encrypt, you're going to need to keep resolving that problem with each app you have or find some other way to tackle it, because you've picked a way to deploy containers, and don't have any kind of centralized cloud system at your back.

In my comments, I mention that the author could have used Kilo, which would have been a Kubernetes-native way to manage their WireGuard system, and to connect the Pi & their other systems to their existing K3S system.

I agree that docker-compose might be simpler, but there's a very very limited realm of concerns that that will ever serve, where-as Kubernetes's / the Cloud Native ambition is to manage everything you would need in your cloud. Whatever you need, should, ideally, be managable within the same framework.

DNS is another decent example, where Kubernetes will help you manage domain names, somewhat. Still work to be done there but there are some good starts. There's so many operators, all of which purport to let you manage these services in a "cloud native" way. We're still learning, getting better at it, but being able to manage all these thing semi-consistently, via the same tools, is a superpower. https://github.com/operator-framework/awesome-operators

Also just the question of short term wins vs long term use. You will not use docker-compose at your job. More and more people are going to be using Kubernetes to manage a wider and wider variety of systems & services, making more and more capabilities managed by Kubernetes.