General

About 120k clean range with 50% boss to kill him exactly on time assuming he did not use much of the skill where his hitbox disappears.

whats the range needed for a lv 172 to solo?

With a range of around 160k-180k and 101% bossing, I manage to get leviathan down to a little bit more than 3/4. I'd say once I get to around a 200k or so range, it would guarantee myself to beat it every time.

EDIT: My clean range is around 100k, and my buffed range fluctuates from 160-180k. I'd say a clean range of 150k is good enough.

If it helps, as a pally, I need to deal 1.5-1.7 mill per line (10 lines) in order to barely beat him (7ish sec remaining).