I took this same port (SDL Sopwith) and ported it to Gamecube a number of years back [1]. It was surprisingly not that hard to do. As you said, most of the work was in the porting to SDL. The guy who did the SDL port was Simon Howard, by the way.
What makes you think that? I don't see that reflected in the rules. "Show" rules say nothing about how much effort one perceives someone put into something.
To quote what I think are relevant rules for this discussion:
"Show HN is for something you've made that other people can play with." - check
"The project must be something you've worked on personally and which you're around to discuss." - check
Show HN is for original work other people can try out and provide feedback. The bar to 'original' is pretty low (a non-trivial port meets it, a Learner's First Project usually meets it, etc) but a straight fork-and-recompile stretches the meaning of 'worked on' to the point of meaninglessness.
You can't really respond to feedback if you didn't make the thing you're showhning.
My point was that it could have been a PR on the original repository, hosted by the original author, and that would have been a nice Show HN even if posted by the person who helped build it for the web. Contribute positively to a good project.
Most of work was already done there: https://fragglet.github.io/sdl-sopwith/
Not even any commits in the fork, it's behind by 7 commits!