You "believe" the electrical code for a 20A line only calls for 12 gauge, and you think it "should" be safer with 10 gauge. You actually mention twice that you think it "should" be safer. I'd love to hear your repsonse when his house catches fire. "Well, I thought it would be ok."
If you're not actually qualified to give factual, technical advice on house wiring, perhaps you should keep your "beliefs" to yourself.
If you're not actually qualified to give factual, technical advice on house wiring, perhaps you should keep your "beliefs" to yourself.