The fact that you 3 stocked him means he either isn't that great to begin with, doesn't know his character's kill moves, or was just not playing well that day (an off-day). Anyway it really depends who your against: if you're fighting pit or sonic yeah, you'll live a lot longer. But other characters like Lucas, or a good ike/ganon will kill you at 50-70%. It's also stage dependent. FD, Luigi's Mansion, and other large stages with high ceilings help preserve Lucario, since he's floaty and dies vertically easier then horizontally. Try the same match on Corneria or another smaller map, see how well that goes. People also think Lucario easy to gimp, meaning it doesn't matter what % you are, you just cant get back on the stage. Also characters with a good spike (no marth, sorry) can turn a game around in an instant.
Honestly, there are times I live to over 200%, but that's usually when I'm on a large stage (or a small one but with a lot of walls) and when my opponent has only a few KO attacks and they're predictable *coughpitcough*.