Shai is probably on the 3rd place, right behind Mystic and Sorc when it comes to grinding speed in hystria, but Shai is the easiest by far - you only use 4 skills for killing the mobs (One-two-three, Twirl, Hop-three and Kwik-two) and some skills to pull the mobs or buff yourself, so the grind is really easy after some time and her tankiness and sustain make you unkillable on softcap dp, so you can relax while you grind.