I love how everyone hates on the MCH story because it's the only one where you're not going into a group of skilled fighters/healers that has a long history to them, and doesn't have the "only a god among men can wield the power" aspect that most of the others do. The fact that Machinistry was designed as a way to allow anyone to be able to defend themselves and their families against the draconic hoards constantly attacking Ishgard, certainly shouldn't detract from the fact that the most skilled MCHs fight on the same level, (though not the same raw DPS as), any other job out there....
Also, unlike the other jobs where you're becoming a member of an ancient, often long forgotten, group of warriors, you're instead helping to create the beginning of such a legacy. As "EdwinLi" points out above, the soulstone you receive as a MCH is blank. You're not relying on the knowledge of others who came before you to preform as well as you do in battle. Instead YOU are the one infusing the soulstone with the knowledge that future Warriors of Light will use to guide them in your footsteps......
EDIT: I'd also like to note a little bit of irony within the MCH questline. The main focus of it is that the job has no respect among the people of Ishgard, and that you're trying to slowly build that up and prove it as not only being viable, but a valuable asset in battle. Sounds a bit familiar to the situation among the playerbase doesn't it?