well actualy I like the Ninja cause He can use blackmagic(mainly haste, i dont use magic a whole lot) and with ice/fire armor and Katana same with with Knight they can heal and stuff and are basicly tanks, Ninja isint hte best Fighter but he can fight and support with blackmagic and wont die at bosses in a couple hits.

Minks are only great and do crap loads of damage if they have haste and are protected long enough to attack, no magic at all and low defense bad.
and he doesnt really gain anything from class change. but he has great potential and is very cheap so you cant complain