This is why we don't take advice from randos on internet.

I manage 100+ variations on a single helm chart and 50+ such helm charts at work daily for 7 years across 11 datacenters/kubernetes clusters. And I have team members who swear by kustomize. The number of kustomize typo errors and issues that I have deal with is unimaginable. Whereas if I test and deploy a helm chart, I know it will work everywhere in every variation.

Kustomize is just plain terrible and backwards as a solution. It doesn't scale, it is half assed. It tries to basically require you to build your own compiler and parser and transform. With kustomize + envsubst: dear friend, you have built helm.