Jotunbrud does not equal large size or powerful build. You count as large for your opposed rolls on tripping, disarming, and seeing if something can eat you, IF it's advantageous.
Jotunbrud does not affect weapon size.
If jotunbrud said "one size larger" rather than "size large" it would be nicely stackable with enlargement, expansion etc. Making the enlarged human count as HUGE if it's advantageous.