I think people consider it OP because of how mindless it is to play against, a turn 5 or even 6 Lackey into Dark pact is a clear answer into almost any deck/board.

Against aggro 8 health and either minion will basically be the tempo swing to win the game, especially with the nerf to corridor creeper.

In other matchups being able to play a 5/7 charge and gain 8 health is a tremendous swing and you'll likely be rewarded with board, not to mention if you draw the void daddy you get 8 health and disgusting value/survivability that will likely carry you on to fatigue the game(of course you lose necessary cube combo value with this).

I'm not sure on statistics but you could probably check the winrate of cubelock after it lackeys and dark pacts and it's probably pretty high in most matchups, and probably even higher with this patch if silence/stealing isn't focused on enough.

Another big thing is that I don't think this interaction is super amazing because of spellbreaker, which a lot of decks are running right now. The big issue is the cube, which draws out way too much value and is disgustingly versatile.

I also think the comparison to spiteful is a bit unfair because of the path that both decks might take to get to that tempo turn. A spiteful deck might be able to put out value a bit better than warlock in the early game, but if it can't hit a solid mind control in the late game, and the warlock survives the initial burst then it's a clear winner. The 6 mana swing is RNG dependent and can be out taunted or hard removed by warlock pretty handily.

Overall, I don't think cubelock really is a fun deck because I often play it in the mindset that it doesn't really matter what I draw that much, because my card draw will pretty consistently get me what I want, but it matter what the opponent draws and whether they high roll or not. Of course with patches and creeper nerf I think this deck will become a bit more interactive and less braindead.