> Yes, but one only needs to write it once...
...and then keep up with behavioral changes that the Systemd Project people introduce and load-bearing bugs that services end up relying on for lifecycle management.
OpenRC service files are easy to write, and their schema is far far simpler than that of Unit files. [0] It's really not worth the effort to write and maintain an converter, if for no other reason than you need to understand the semantics of both systems' service files to double-check the results of the converter.