Ok now this would end up in a deep philosophical discussion if done right. Even if open source it is good tone if not obligation to mention the work that has been done by others, if you make use of it. Branding is a difficult thing and Bitcoin Cash, for example, has done nothing for its branding except for ripping off the good parts of Bitcoin without mentioning them properly, while shedding a light on the seemingly bad stuff within Bitcoin and presenting themselves as those who have the proper solutions. I don't like that approach (but I know this whole thing is not about taste, so my opinion is worthless, sadly).