I don't think Lackey has much on Ruthless. It has a better d1. It can burn meter for bigger combos/punishes, but the thing is, Ruthless doesn't need to burn meter to punish as well or better than Lackey. So if you downplay Lackey's EXdb2 in this comparison, all Lackey has is the d1, which okay, is pretty fantastic. But still, I don't really think the d1 by itself fully compensates.
Ruthless in exchange gets all the benefits of Ferra. Ferra Toss, Bowl Girl, longer range, faster b2, fullscreen NJP, PnG...
But if for whatever reason you aren't interested in Ruthless, Lackey is different enough from Vicious that it has it's points.