whirlwind is definitely worth it only if your centred and fighting unarmed.

you get the bonus hits, usually 4-8 hits per whirlwind attack with decent doublestrike.

if you are using a weapon, you get half those (2-3 hits if your lucky) with GTWF etc etc.

Yeah it can be a fun build to tinker with, but it is definitely not optimal.  Sadly unarmed is still pretty gimped in DDO.  And kensai gets a lot of bonuses to "equipped weapon in your focus".  And even though you take martial arts, technically handwraps aren't a weapon.  Lol.  So the crit range and modifiers etc don't actually stack. 


But that being said, play what you want to play.  If it was me I would go 12 monk 6 fighter 2 rogue.  Bonus SA dice from ninja assassin, full trapping, Shintao double strike and prr, and kensai for the rest.