Ok, let me put it differently then.
On hard or higher, I'm not even sure a pipe bomb could even kill a scrake when used by a non demo. Yet if you use a weapon specific to your perk, you can kill a scrake quickly (handcannon + SS, katana + zerker, 2 shots from a hunter + support, etc etc).
Pipes do large spike damage as a demo, but you can only carry what, a max of 10 at level 6? And there's no guarantee you'll hit a hard target with them (good chance a group of clots/gores/etc will stumble acrossed them). Unless you risk yourself by waiting for the target to be in front of you, and throw a pipe or 2 while back pedaling, and hope it doesn't charge you or that a group behind you doesn't pop up and blow you to bits with your own pipe. Otherwise it requires time, planning, and luck to get them into positions to actually hit FP's/Pat/etc.
Also I heard a rumor that pat no longer can be 1 hit KO'ed by pipes. Dunno how much truth there is to that, but I've seen him run over a mine field of 20 or so and still run off to heal.
Sure, Xbow is OP and a bad comparison, but 'till it's removed or nerfed it's still in the game and usable by most perks (firebug doesn't have room for it), and it's a much more efficient way of taking out hard targets, including Pat. And when you're talking balance, you have to compare against all other options.