No one is judging you parenting style. To me though it would seem that taking away the system or making it unusable would be the same as getting rid of his internet access and the consequences of doing those would be the same unless it's just a matter of keeping him offline so he plays only single player games (I've met my fair share of those heavily addicted to online/MMO games, 14+ hours per day, calling out/losing jobs, etc).
Getting back to your original question if your phone does have a unlimited data plan you should be able to setup a personal hotspot with password and use that for the online access for your other devices. While this probably won't be as good as your regular wifi this is the simplest method I'm aware of. Change password on a regular basis to keep him offline.