OP, I don't mean to hijack your thread, but I have been wondering (and kind of agonizing over) the same thing (re: quitting piano) and could use some advice.
My DS is 6, close to 7, and last year asked for piano lessons for his bday. I didn't feel like we could say no to that so we started last summer. We got a keyboard (which meant we couldn't do Levine, and like PP, I was kind of turned off by their take), started lessons, and he has been pretty into it....until about 3-4 weeks ago. He now resists practice, a lot, and wants to quit. He never argues about going to lessons and once he's there he's really engaged.
I can't tell if this is just a brief phase we should push through, or if this really means piano isn't for him. Like you, OP, we are not super-scheduled and in general we never do more than 1-2 activities per week. His teacher is very low-key and asks for about 15 minutes of practice per day. DS is decent but definitely not a prodigy--but I don't care about that, and neither does DH!
For us, it's more a question of, do you make your kid stick it out (at least until the 1-year mark, to which we're so close)? Or just give up, at least for now?