Actually, that is not necessarily true.
Gallade and Lucario are NOT meant for the same purposes. Lucario is a sweeper of many sorts. Gallade is for more bulkiness and support. Gallade can take way more hits from some of those extremely common attacks, and can take at least two super affective hits if he is used CORRECTLY. Too many people are trying to use him as a sweeper. I have experimented with many different ways to use Gallade, and he is just not a sweeping type.
Another thing about Gallade is that, unlike Lucario, he doesn't have a million counters, giving him a fighting chance. Lucario is easily countered by the likes of Gliscor, which takes the dog down with a single Earthquake. Gallade, on the other hand, and survive one Earthquake from Gliscor, and take it out with a good Ice Punch.
Lucario may be faster, but Gallade can learn moves such as Thunderwave and Will-O-Wisp, which Lucario cannot. Though this may sound a little ridiculous, you should think about it. Gallade can cover his poor speed with Thunderwave, or he can cover his poor defense with Will-O-Wisp, as burn cuts attack.
So, all in all, Lucario and Gallade really aren't meant to be compared like they are. They are too different. In my opinion, they are about even.
I am not saying this just willy-nilly. I am saying this from both research and experience.
I rest my case.