The luck in 9 ball doesn't come so much from slopping balls. It happens, but more often than not in amateur play it's followed by a miss rather than a run out in the next couple of shots.
The luck factor is more to do with where players are missing and what they leave when they miss.
I find it is often that one player continuously misses on the 6,7 and 8 balls leaving his opponent 3-4 ball outs. The other player on the other hand may consistently miss and leave opportunities on the 1 or 2 ball always leaving a full table to run, which inevitably leads to the missed 6,7 or 8 ball. Now obviously you can say that better safety play needs to be employed, but that's easier said than done!
The other issue is that one player may constantly be leaving long tough shots, off angle shots or hooks after misses (not including two way shots). The other player will be leaving bih type shots.
Now this is more typified by amateur play, but I do see examples of it in the professional game too.
How a game where you can win a game by pocketing one ball to your opponents 8 is contested seriously by professionals, escapes me. I'll never understand what the problem with Rotation is.
I've had some pretty bad luck in Snooker and 14.1, but nowhere near the frequency in 9 ball.