It’s the exact same story in Aviary and Library from my experience and that if my wife and son.
I made it into Library about five months ago, and have just about managed to stay in there. I’m generally between 5100 and 5300. My wife who is way more about using dinos she likes sits between 4600 and 4800 and my son between 4800 and 5000. None of us seem to be able to move out of these brackets.
We have all played pretty much since the launch and don’t spend much money on the game.
The alliance championship is a welcome addition, we all love that. And we are looking forward to what the co op will bring.