DIY NAS totally not worth the time, money or effort.
Off-the-shelf NAS use ARM or specialized Atom hardware for extremely low power consumption when idling. Ridiculous to use desktop-grade hardware that drinks power like there's no tomorrow for home NAS use. Even enterprise NAS with 4 to 8 disk bays can comfortably run on Atom hardware.
DIY NAS is also limited to the home network. Unless there is an existing VPN setup at home, I rather sink $4 for a monthly cloud subscription with 100 - 200GB storage and access my digital items everywhere with guaranteed availability.
I rather install ESXi on that G5400, load a Sophos UTM virtual machine over it and use it as a high-performance gateway + firewall. Or do a baremetal install pfsense for a honest-to-goodness Unix-based firewall.
It depends on what you are using the nas for. Personally, I'm using mine as a personal media server + personal file storage. I agree that desktop chips are not recommended but SOCs are perfectly fine and it's good enough for me to stream 1080p videos on 1 stream(I'm the only user after all).
Off the shelves nas for media server costs a bomb and they usually only support raid which is also not ideal for me as as I have multiple HDD with different sizes which I want to make use of.
Also, these data are expandable for me so why would I sign up for a monthly subscription for backup services? They also don't support video streaming and those which does(google drive) cost a bomb for limited data space.
Fyi, I have about what 30tb or more video files.
Diy nas has its market it just depends on what the user is using it for. Please don't give a blanket statement and say not worth it