[wahern]

-f is guaranteed by POSIX, and #! is de facto portable.[1] My criteria for shame is, "will this silently break in the future?". I think you're good. It's not my style, but if it were something I came across at work, so long as it worked well it wouldn't even cross my mind to try to "fix" it.

FWIW, using make -f in the shebang is also done for debian/rules in Debian package builds. I don't know if it serves any real purpose. I suppose it permits one to write a bespoke script for building targets without using make.[2] I guess I wouldn't be surprised if someone, somewhere depended on that capability, given how old and widespread Debian packages are.

[1] /usr/bin/env make -f would be better, but then you run afoul of the problem that you can't portably pass more than a single explicit shebang command argument.

[2] Which I see now is a bonus to your process-data.mk script. It could be replaced with a non-make version without effecting callers.