You spend lots of money, you can play any hero you want...and get gear / levels / credits ect. faster as well. Also when a meta changes P2P can adapt and change heroes and squads when it does...and not wait months to catch up. RG is a good example.
A lot of heroes are a very difficult farm and very time consuming, people pay to use Rey "right now" instead of in 3 months. What happens when there are balance changes and all these farmed F2P slowly get pushed out of the meta via buffs and nerfs between heroes? Or new heroes are released?
Also, not sure paying in games should make you "stronger" than everyone else. It seems paying in this game let's you experience a lot more with heroes. I have plenty of heroes that are waiting to be leveled and geared, but a pure P2P can spend to get them there. I have a 7* poggle and 86 at level 1 with no gear, I simply cannot afford the resources to get them playable yet..a P2P can.
Also, once more game modes are released the weird fascination with Arena might diminish. Arena has the best rewards, but based on the A.I. it isn't too difficult for anyone to climb the charts F2P or P2P regardless of squad. If A.I. got an overhaul and other challenging modes are released, expect to see F2P lose traction.
Paying money keeps you ready for changes and quick shifts in game balance. Looking at this as a snapshot in time is fruitless. Just now people are getting their QGJ leveled up since he became F2P, P2P has gotten to enjoy his dominance for a while.
Full disclosure I was a medium to high spender in this game and have since stopped spending as I felt my $$ wasn't worth much in this games current form.
