I'm in the humanities. I don't know what the difference is between a scientific paper and a history dissertation, but it seems like both could be done, with the caveats mentioned above. I don't think there are many use cases where the iPad is absolutely wrong. If push comes to shove, it can even run a Mac remotely.
Which app would you use for writing the dissertation?
Pages is not capable of handling references etc. well.
I don't know how powerful MS Word is on iOS + you must rent the software and use their ****ing cloud.