It should be you start at 0 trophies and you rise normally, but once you get your 8th highest dino to a certain level, you can’t acess some arenas anymore, your 8th hghest dino ciz it cant be lowest team member cuz then players could cheat the rule. You can still acess the arena if you have certain level dinos but haven’t passed it. For example:
Training Ground: once you pass it and get your 8th highest dino to level 1, you can’t access it anymore.
Fallen Kingdom: once you pass it and get your 8th highest dino to level 5, you can’t access it anymore
Mt. Sibo: once you pass it and get your 8th highest dino to level 8, you can’t access it anymore
S.S. Arcadia: level once you pass it and get your 8th highest dino to level 10, you can’t access it anymore
Nublar Jungle: once you pass it and get your 8th highest dino to level 12, you can’t access it anymore
Badlands: once you pass it and get your 8th highest dino to level 14, you can’t access it anymore
Lockdown: once you pass it and get your 8th highest dino to level 16, you can’t access it anymore
Sorna Marshes: once you pass it and get your 8th highest dino to level 18, you can’t access it anymore
Jurassic Ruins: once you pass it and get your 8th highest dino to level 20, you can’t access it anymore
Lockwood Estate: once you pass it and get your 8th highest dino to level 22, you can’t access it anymore
Aviary: once you pass it and get your 8th highest dino to level 24, you can’t access it anymore
Lockwood Library: once you pass it and get your 8th highest dino to level 26, you can’t access it anymore
Gyroshpere Depo: once you pass it and get your 8th highest dino to level 28, you can’t access it anymore
Nublar Shores: once you pass it and get your 8th highest dino to level 30, you can’t access it anymore
With this, you could switch the backgrounds of each arena
I don’t think you should be locked in once you unlock, you shouldbe locked in once you hit a certain level of power