It's a geometric pattern, lvl and def % increases like it and leveling up is the reverse. Higher your lvl more XP you need and the bonuses you get from lvl increase likewise. Players have a lvl limit on an expontial graph we'd never ever hit max level :/. 

Lvl changed 3 updates back and while it is OK for people under 100 it is causing massive problems past it. Things that go past 100 get very powerful very quickly. It's like doubling values each lvl,  gives a little bonus when lower but super crazy values at lvl 200+.

It is also the reason why arenas are impossible now and High lvl bases that have stuff from lvl 160-220 are just a big no no. Intermediate lvls can range from 90-160 are that's honestly not right, 70 lvl difference on a geometric scaling is just wrong.