I haven't found improved defensive stance to be much use at all, even on Hydross. I reallocate those 3 points to making imp heroic strike 3/3 and imp sunder armor 3/3. That leaves 1 extra point you could pop into imp shield wall.
I use a build very close to that. I took away 2 points from Improved Shield Bash and 3 from Improved Def Stance and placed all 5 points in Cruelty. It is a very effective build for heorics and as an OT in the 25s. It also did not do too shabby while duel-weilding Devastate spam while grinding dailys for SSO rep.