6 is a bad number for a bull unit, it's halfway through 4-8 (3-7 with a caracter), as you don't have enough toget a rank of maximise the number of attack you can get, and not too few to simply use as flank or throw away units.

witht he way ogre magic works, a single caster works best, as all is spells cast on 3+, so switching the butcher for a bruiser for better leadship to the bulls.

Also split your leadbelchers in 2 units of 2

 

I like Units of 5 to go with a character. Without a character Bulls should be either units of 3 for flankers or 8 for hammer units.

Besides that the list looks nasty, and very similar to mine in many ways. One suggestion is to split up the leadbelchers into 2 units of 2 belchers each. It's much more effective.