I think you have it backwards in two ways:

1. While Helix dev is on the slow side, I think what you’re describing as specific to Helix is in fact the typical case in open source

2. In this case the author did a bunch of work up front and the maintainers said no almost immediately after the PR was posted

I agree they could be faster to say no, but I think part of it is that the maintainers would have to agree themselves and as far as I know they are not getting together to come to consensus about random Helix PRs every day.