For any open-source projects, "merge request" is a courtesy from the contributor. If they don't meet the standard practice of the project, then it is fair to say that it can simply be rejected, on any ground or even without any reasons. So if the contributor happens to be "not-so-happy" about this, then one is free to fork and maintain it where it deems fit. it is a fair game, there is nothing personal. Frowning on forks that do not contribute back into the mainline isn't really the right way to deal with GPL. I think this is a fair criticism.
Praises & criticism are just two same faces in part and parcel of lives. Intel's CEO in 2006 who won the heart of Apple Computer to use Intel's CPUs were once helmed as one of the most successful CEOs who put Intel Architecture at its height. He was also the same CEO that championed the ideal of "One Architecture" and sold StrongARM/XScale/PXA/IXP to Marvell to drive the entire company to focus on just one architecture, the x86. Today, the media humiliated the same CEO as the CEO who rejected Apple's request to build a CPU for IPhone, leaving the door wide open for Apple to collaborate with Samsung for the 1st ARM CPU used in IPhone. And Apple eventually took the matter on their own hands, the rest is history. When Apple was in its worst financial deep-shit at the brink of bankruptcy, the founder of Dell Computer, openly despised any values in it and if he would ever acquire commanding stakes in the struggling company, it made the most business sense to split it up, sold it and shut it down. Again, the rest is history.
One of the greatest values in life is to be able to fence off challenges one after another, each time rising ever stronger than before, welcoming the cheers of one's supporters while respecting the jeers of one's naysayers.