I used to think it was fine to take someone else's contribution and then create a total rewrite of it in my own branch and merge that. Or to go into someone's PR and push a rewrite into a new commit on Github. At least in the latter case there'll still be a contributor credit (`Co-Authored-By`), but someone had to do the same with me for me to realise that it kinda sucked and really soured the experience of being a contributor. In my case, it was that someone 'forked' my project by dumping the code into their own repo without any of the commit history.

As you say, even if the code was shite, the refactored fix that got merged in would never have existed without it. "I like my version better," feels pretty dismissive and regardless of any other fact I can see how anyone would feel a bit miffed about that after they put the work in.

Edit: the reply linking to the actual response from the maintainer invalidates my last sentence.