Donsan
Your point about transmitted power is of course correct. But Furuno MFD8/12 MFD, which can run some of the smaller radars, need 10/20 amp fuse respectively. And another 3 amp for the Navnet sounder. So a lot more than you could get from N2K.
The question is whether the Garmin models that fit your limits can provide good enough output, something that is a personal choice. Furuno NavNet data is over ethernet, and once again you could do WiFi if you accept quality trade-off.
I think you need the successor to N2K, which is getting dated and as you note has serious limitations.