I WISH my dog was tug motivated, but ball is all I've got that really puts her in drive for energetic OB. Food used to work better, and still is good for working on precision. It holds her attention but doesn't build sparkle as well.
It may be something to build on. As a youngster, my dog was not super motivated for anything except food. His drive for the ball (and subsequent reluctance to out it) is definitely a monster I created! When I first got a ball-on-a-string, I would throw it, he would chase it, then just trot away from me and lie down very nonchalant. It took a LOT of two-ball to get him interested in coming BACK to me to engage, not just carry the ball around while doing other stuff. Finally he started coming back but liked to play keep-away if I reached for the string to tug, so I trained him to jump up on my chest and shove the toy *into* me, which works great for playing together as long as I am paying attention
I also did some back-tying and teasing him with the ball. The more I made it THE fun thing, the more it became HIS thing. I had to do the same for other toys, take a few steps back and show him that those are fun too, they can be fetched or tugged or whatever. If I take a few minutes of playing before going into some ob, he'd work for an old towel, but early on I had to really build his understanding that everything is more fun with me than just grabbing the object and running off. He was not real into tug either as a pup, but now will tug anything, with anyone.
But, I do agree that using a ball was always my preference for ob training. I liked having something I could easily hold in my left hand and something that I could drop, throw, tug with, etc.