Disagree there Kabooa. Machinists would almost certainly completely vanish without disembowel, based on current upload numbers they have with it. MCH trades off BRD's level of support for personal damage, seen in hypercharge v foes + battle voice + passive 2% crit buff, and it doesn't pay off well for them at all.
"Should a bard not be present or available" is a unicorn. I say that knowing full well I am that unicorn. However you are saying "should the most popular job in savage be unavailable maybe we can find someone who mains the least popular job." Also without piercing I have high and heavy doubts you'd ever see mch/brd in a serious comp again.