I agree that balance controls on DACs are rare. However, the Lumin App which controls my Lumin X1 streaming DAC has a balance control. Still, I almost never use it. I haven't had any use for a balance control in my systems for decades. Any well-set-up two-channel audio system like mine is optimized for best sound from a single chair so as to create a precisely centered and focused virtual center image on normal mono and stereo recordings.
In fact, one of the best ways of testing your set up is to determine how precisely center focused a phase-correct virtual center image is perceived from your listening sweet spot. The set up isn't "right" until you achieve such focus.
Alternatively, you can also test set up by maximizing the diffuse and directionless quality of playing back a monophonic signal where the absolute phase of the two channels is intentionally 180 degrees out of phase. Some test tracks do this, or you can switch the hot and ground wires of one speaker cable to do this with in-phase source material.
If in-phase images intended to be centered sound off center to you, then it's most likely that your physical set up needs work. An electronic balance control won't ideally fix what is wrong with the imaging. While a balance control may help get the center image to be perceived as centered, it won't really sound correct because the balance control cannot correct for the difference in time of arrival of signals from speakers which are not equidistant from your ears. The center image may seem more centered, but other aspects of staging and imaging still will not sound correct.
And if the speakers are truly equidistant from your ears and you still don't hear a centered image, then the problem could be a personal hearing issue, equipment related, source related, or--again--physical set-up related. For example, a listening room which is much larger or more open to one side--not left/right symmetrical, in other words--will often cause the channel on the larger/more open side of the room to appear softer from the listening seat. As opposed to tweaking a balance control, a better solution involves changing the system layout to make the room left/right symmetrical and/or listening in the near field where the listening room has less effect on what you hear from the sweet spot.
As an example of a source-related balance problem, I recently encountered an internet radio station whose signal sounded left/right balanced for years and only recently seemed heavily weighted to the left. All other source material sounds balanced. I concluded that it was an issue at the station and I wrote to the station's technical help line requesting correction of the problem.