[spicyusername]

This is exactly what I'm talking about.

Using variables isn't supported in backends - e.g. "niche places" (although it sounds like it is in OpenTofu)

And #2 and #3 are exactly the use-case for just regular old tfvars files and module imports.

Terragrunt encourages you to abstract things way, way too far, until you have an absolute mess of tangled imports and deeply nested directories.

Nothing wrong with having a root module, some child modules, and a single tfvars file being fed in on the front end.