Sometimes the limitations of kustomize annoy me, but we find ways to live with them
We do package our own helm charts, not in the least because we sign contracts with our customers that we will help them run the software we're selling them. So we use package docker and helm artifacts that we sell in addition to running locally.
So we write some charts that don't use most helm features. The one useful thing about Helm that I don't want to live without is the packaging story. We seem to be the only people in the ecosystem that "burn in" the Docker image sha into the Helm chart we package, and set our v1.2.3 version only on the chart. This means we don't have to consider a version matrix between our config and application. Instead we just change the code and config in the same git sha and it just works.
Replacing with hash is a neat idea, might start doing that too.