Leviathan shouldn't be too bad at our current PL. It also is step we all need to do to get higher than 350PL.... (post milestone completion).
I have beaten it a few times but will be rusty as all hell (especially the game show part and Calus). Dogs and pools are easy once you designate where everyone is going.
The more I think about it the more I believe the current leveling post 345 feels broken. Why are we only getting 340/345 drops from 350+ PL activities... This doesn't make any sense what so ever. I am wondering if the current PL was increased at the last minute (from ~360ish) but the rest of the game hasn't been updated to factor this in. Based on the raid PL we should be hitting 355-360 (10 below Raid) before the real grind kicks in.