Note that while the undead summoned by Master of Shrouds are numerically weak, the vast majority of even high-level monsters don't have substantial means to deal with incorporeal undead (best methods likely being some sort of blasting SLA, which have a 50% chance to fail completely). The only reasons Master of Shrouds isn't a very highly favored class around these boards are the lost caster level at 1st and the Summon Undead IV and V spells, which essentially duplicate the Master of Shrouds class on a fundamental level.