The thing is, when you aren't using the admittedly cheaty EE2, it is better because you're making loving diamonds.
Yeah fine.
Actually the cheaty bit of the admittedly cheaty EE2 doesn't feature in the use of a Mass Fabricator, only the condenser which whilst you can generate diamonds from dirt isn't generating diamonds from air/light.
Besides, the reason EE2 is considered OP/cheaty is because you can generate diamonds and crap from nothing. Solar panels might not be cheap, but by solar powering a Mass Fab, you're still making diamonds from light.