I can see your point of view, but IMVHO there’s no inconsistency.
Try to think NethServer as a car. And ClamAV as an optional of an optional. IDK… a USB-C set of ports of the rear seat central armrest.
The counter-intuitivity of the car example is that you don’t add and remove optionals as you need during the life of the car but… Try to follow the think please 
Maybe for 3 months you don’t need the USB ports in the back of the car so for saving fuel and energy… you remove them. Maybe for 6 months you don’t need the armrest in the back seat (car became a lorry) so you remove the whole seat and the armrest. In that situation, you cannot install back the USB ports… you don’t have a place to put them!
In a similar way, ClamAV is useful only if the server receive and make available data, so MailServer, FileServer, Proxy. If you want you can install it, but only “following” the primary modules.
Also, GUI sometimes have to come to compromises, so a “good for everything” is still a goal, but hard to achieve.
Probably your system is powerful enough to drive all your needs, unfortunately… ClamAV is designed for one thing only.
(Nice. I now know that OpenSource community have to thank Cisco for ClamAV, because brought Sourcefire in 2013)
And sometimes… ClamAV, especially with large definition file, is… inefficient.
So following 1GBE internet traffic could be… A tough job, even with a nice consumer CPU like an i7 mobile.