Fawkes is stupidly overpowered, yes, but the thing is, when I got him the first, there was nothing left but a bunch of supermutants I could two shot with ol' painless so it didn't matter much.  And the second time he joined, 95% of the fightining was done by the giant robot.  Even I had trouble finding things to actually kill with LP around, and I can stop time.  Not much use to be superpowerful when there is nothing left to kill.
Big guns are useful for 1 reason alone.  The flamer.  If you take that and the pyromaniac perk, it becomes a roomcleaner.  And really, pyro is a very nice perk.  50% extra damage is never something to sneer at, and it covers at least 3 different weapon type - melee, heavy, and energy (the special alien blaster).
Plus, splash damage doesn't tend to disrupt sneak like direct does, so you can be a rocket ninja.  Yehaw.
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