All players are see Solo leveling(2moons gold) hard up to a point. After so long though, you have enough aoes (especially with the right build) and a good enough summon to make it a lot easier on yourself. It's probably hardest from 48ish to 52. Exp req jumps and you dont have an aoe.
If you want to make solo grinding isn't hard for your character, dmg build or heal build can do fine if they play the build, we were able to solo the back of aqua fairly easily at level(2moons powerleveling) 115 with out amazing gear and +4 staff.
After we have reskilled a +7 tb and 4-6 armors in 2Moons, we can solo parts of AR and space fairly easily at 13x. If you happen to have resistance sets, fast kills and u take almost no dmg when ruins is incredibly easy.
Summoners are better for pve, but in high level maps mages take the cake because the can pwn everything so fast, not to mention they have pretty good defense for being a DD.