[FSLAR]

It's worth noting, on the Lucario and Terrakion comparison, that Lucario has less weaknesses and more resistances(though its defenses are non existent) and the only priority move it is weak is Mach Punch, while Terrakion is weak to Bullet Punch and Aqua Jet. In fact, Terrakion only resists ExtremeSpeed and Sucker Punch (which doesn't even count because that would do far more harm than good); Lucario resists Bullet Punch, Ice Shard, Shadow Sneak, Sucker Punch( both extremely rare but still). This becomes somewhat moot for both Pokes after a Defense drop, but the point still stands. And of course, ExtremeSpeed and Bullet Punch compensate for this with Lucario. Terrakion may have decent defenses but the myriad weaknesses work against this, though the boost from Sandstorm definitely helps. It is worth noting that because they have a different set of resistances, this sets them apart, or can.
Also, Terrakion cannot beat Gliscor outside of Rock Gem +2 Stone Edge - which can still miss as Gliscor Earthquakes you - but Lucario can with Ice Punch - without a boost sometimes too.