It sounds like you don't know how the Bash/Zsh ideas I mentioned work. They run the command with --help, parse the output, and from that generate the completions, wiring them in to the completion system. That method is a zero config solution (well, you might need a list of such "command-names only" - no option names, which could change at any time -- so maybe "minimal config"). The OP & you mention a much heavier config solution which strikes me as against the vibe of Fish in general which is, supposedly, out-of-the-box niceness.
It sounds like you don't know how the Bash/Zsh ideas I mentioned work. They run the command with --help, parse the output, and from that generate the completions, wiring them in to the completion system. That method is a zero config solution (well, you might need a list of such "command-names only" - no option names, which could change at any time -- so maybe "minimal config"). The OP & you mention a much heavier config solution which strikes me as against the vibe of Fish in general which is, supposedly, out-of-the-box niceness.