the first part of the mainline quest area, you're looking at 3 subs from 3 diff starter caves/areas and they don't do that much damage, they are just tanky.
Bosses in ideal grinding areas after the first main questline area (you'll finish around 45), any subs with decent loot (around lvl 65) are pretty much impossible for any class to solo until you get to that lvl yourself. As an example subs Crystal Spider and Minotaur Sub do high damage to pets and mino sub lightnings at range!
Nobody is doing subs properly alone comfortably until they get to a very decent lvl (75+ starting 'd say), FYI sins aren't reliant as on other servers to be chasing after subs for cash, there are some great areas for you to explore, my favourite place in this game for example is amazing for Tao's and Sin's.