But a real "Amiga enthusiast" wouldn't be using OS 4.x, a real "Amiga enthusiast" would be using genuine original Amiga hardware and doing everything possible to get the best out of it... 
In your opinion, and your opinion is not necessarily the same as the next guys.
Different people have different ideas about what makes an Amiga an Amiga. For some, it's the original hardware and software, or others it's mostly just one or the other. For those that regard the hardware as the quintessential factor, the MiniMig, FPGAArcade and NatAmi are the obvious evolution. For those that regard the OS as the main aspect, then one or more of the above NG OS are the logical evolution and what they run on is of secondary importance.
The only reason "NG" amiga operating systems exist at all is because enthusiasts have made them happen, whether they are commercial (as in the case of OS4 and MOS) or not. I doubt you could find a single developer that has worked on OS4, MorphOS or AROS that isn't or was never an avid enthusiast of the original systems.