most likely because this device is mainly for wifi use, and/or limitation of the SoC.

You want your $90 wi-fi router to do what now?

I can't tell if WAN is Wireless Area Network or Wide Area Network.

Given the 2.5Gb port also supports PoE in, I think the idea is that you can plug this into a 2.5Gb PoE port on a seperate managed switch and that's the only connection you need; that's certainly how I would use it. WAN connections could be plugged into that switch, along with the APs, user devices, servers, etc, with them seperated using VLANs. Assuming everything was gigabit except for that 2.5Gb link to the OpenWRT Thing™, you'd be hard-pressed to saturate that 2.5Gb port and you'd still have the gigabit port completely free for... whatever.

Nerd here. You confuse me:

WAN is some up-/downstream port connecting intranets remotely in my novice book. The measurement G doesn't refer to some advertisement-thingy in terms of wireless speed (but Gigabyte) - Maybe it's some form of Generation; But then I lack everything including my false base knowledge. Additionally I have never encountered "2.5G LAN" ever before: Would you be able to shed light on my shortcomings? 2.5 x 8 is 20 Gbit. I didn't read about that size yet.

Edit: Thanks guys!