The tone is very poor. "This is bad: closed" is not a friendly way to communicate and attract contributors. There are obviously better ways of encouraging contributions to match quality requirements/project style.
I read it all... it is hostile, the MAME owner clearly can't be bothered and just wants to close it, and while I can empathise with being inundated with PRs, it's still possible to be accommodating without actually donating much time, you just need to point people in the right direction. and in the event that something is fundamentally incompatible with the project (which this is not) you can show a little class.
The patch came in barely working (not compiling on all platforms) and hacked together. Anyone who's worked on a long lived code base knows good architecture is important.
They explained what was wrong and how to architect it cleanly. It's not the responsibility of the MAME developers to do his work for him.
They also reasonably discussed the utility of supporting his niche closed hardware. Remember once the code is in tree it's their responsibility.
Also the hostile treatment he got from the MAME developers is kind of amusing: https://github.com/mamedev/mame/pull/483