I call bullcrap on this one. What part of FB have you been hanging out on? You must be in some other FB world.
In the "online world", there is a much larger tendency to gripe about something than to praise it. These forums are a perfect example - it's a breeding ground filled with complainers and whiners and anyone else who wants to grind an axe. If anybody tries to present an alternative positive view, they are labeled a fanboy. If the number of "fusion happy" people outweigh the number of "fusion unhappy" people on here, you can bet that in real life they outweigh them even more.
It's safe to say that Fusion has been a technology advancement that has been viewed very positively by a large number of users. It's mainly dissed by the self-proclaimed "power users" who may be a little OCD about where every one of their files are stored. There are some (video creators for example) that may not see as much benefit, as they frequently may be moving very large files around, and the 4GB Fusion buffer gets saturated quickly for them. But for most folks, it's a great way to experience SSD-like speed in a 1TB or 3TB arrangement.