Pokemon go is incredibly friendly to casual players. everybody gets everything. The only place where players interact via the game is at gym battles which are heavily heavily biased toward the attacker. Level 15, perhaps even level 10 can take down anything, given enough potions and revives.
If nothing else, Niantic learned from Ingress. High level players have high level stuff, sure. But 6 v 1 ensures even the most casual player can make progress. You don't have that level bonus wall to climb that you have in other games.
I gave up because I didn't know that was the case. Nothing in the game indicates it's like that - all I knew was that my Pokemon had far less power than the ones in my local gyms. I suspect most casual players will be similar as the game tells you very little about how to get the most out of it.
It wasn't so friendly for me. I took my kids out Pokemon hunting in the car and we drove around for a while looking for one. My son was traumatized when we drove over a pidgee. I'm never doing that again!
If nothing else, Niantic learned from Ingress. High level players have high level stuff, sure. But 6 v 1 ensures even the most casual player can make progress. You don't have that level bonus wall to climb that you have in other games.