The delay isnt all the problem about it, time to get the weapon out (shuriken) make the throwing motion, get the melee weapon back... All that make too much time. Haste and double attack don't stack either. Now with all the Dual attack, Double attack and haste gear, meleeing still the best option and I would rather improve Dual wield Via merits than Sange.
Sange could be only used in, well, no situation at all... (you didn't prove that Sange is usefull yet, sorry).

I would like Dual Wield Merits instead of sange. If you don't agree Dual wield merits could be more effective than Sange, well, I don't know what to say more with all argument we provided VS pro sange user, who never proved me yet, I should invest Merits in that useless job ability.