it's actually not THAT hard to level... you just have to be in a populated area and spend some time on it. My buddy is level 16 and has spent $0. He just plays A LOT lol
I'm level 6 already, but feel I've played quite a bit (three 3-4 mile runs, stopping for them as I go, multiple long dog walks).
Your friend is only going to get stronger faster than everyone else too. I think they need more incentive for regular folks, or they're going to slowly fade away as the gyms are just locked down.