> The only tedious thing is you have to adapt this for every image type you run.

The tedious thing is that this escalates into complexity whenever you have to deal with K developers using M projects developed by N teams each using a different way to handle this:

Do I need to set USERID for project foo, or UID? Does it default to 1000 or the author's UID? Oh, someone has a problem with our project, did they remember to set COMPANY_USERID in their bashrc? Oh, wait, they're using zsh, how do you do that there? Oh, but they followed this other project's readme and that set COMPANY_USERID but not COMPANY_GROUPID...

Docker is supposed to simplify this by unification and a limited API surface, and applying hacks like this on top kind of kills that whole premise.