Having recently replayed FF9, I had Thievery doing roughly 4500 end game. I think based on Zidane's Speed, that means he stole about 300 times total? Honestly don't remember.
I wasn't meticulous about stealing, mind. Zidane would mostly steal in fights where his turn wouldn't matter (ie the other 3 characters could kill everything without his help)...which is pretty often considering FF9's style, barring that section on Disc 2 where he's your only physical fighter (aka only source of MPless damage <_<.) He did have higher speed than the DL, but I think I remember compensating for that (alternatively, if Thievery WAS Zidane's primary source of damage, he could use a speed boosting weapon like Orihalcon or something.)
In any event, Thievery at best is only marginally stronger than his physical for these purposes. This isn't to say that it wouldn't be useful, mind. Thievery suddenly lets Zidane have Defense Ignoring, and can make use of more Soul Blades like The Ogre's Blind or ones that cause Sleep/Confusion cause I don't think Thievery knocks enemies out of that status, not to mention it gets Zidane around Evade and such.
Basically, Thievery being roughly even with Zidane's Physical is about the extent I'd see it in the DL, though even that would be a huge help just cause Thievery is so much more useful utility applications that a physical doesn't.
The "It wastes time on randoms" thing, as I noted, is a shaky argument though. Again, FF9 has *4* PCs, and typically, you can kill entire fights, especially second half of the game, with the other PCs. Bandit gives Zidane a 100% Steal on his first shot (so long as the enemy has a common steal), so nabbing an item isn't too tough. Also, there are some good items from randoms here and there (summon stones, Ethers, etc.) I'm not saying "YOU MUST DO THIS!" or something, just saying its more reasonable than you're giving it credit for.
