I've embraced kustomize and I like it. It's simple enough and powerful enough for my needs. A bit verbose to type out all the manifests, but I can live with it.
This is what I've done too. Just enough features easily available to handle everything i've ever needed in the simple deployments I use. Secrets, A/B configuration, even "dynamic reload" of a Deployment for Configmap changes.
Gets the job done.
I'm using sed on my yaml files. Currently considering kustomize instead, but I wouldn't touch Helm with a 10 foot pole.