It's highly unlikely the WiFi degraded, and more likely that Wii Us in all their drivers and code don't like your router.
Get a Wii U Ethernet adapter off Amazon and an Ethernet cable. Problem solved.
Source: I had a very similar problem before.
How does a console do that. Its been connected to the modem (with built-in wi-fi router) for over a year now.
Anyway, I live at someone else's house and they don't like the idea of a 100 ft. cord stretching across the inside of the house where it will cause sombody to trip and fall.
That settles it, I'm getting a new Wii U.
UPDATE: Just checked the Youtube app, the videos load much quicker.
How is that possible for the app videos to load just fine, but viewing them on Youtube via the internet browser is a problem due to the slow loading the video goes through?