Pretty much. The assumption is often made that tens, twelves and fifteens each have a characteristic tone and/or frequency response, so using one from column A and one from column B will give you a 'best of both worlds' result. That assumption is just plain wrong. There is no difference in either tone or frequency response that can be attributed to driver size in and of itself. Where the average musical instrument driver is concerned there's actually very little difference between the three sizes. But there are differences in the phase responses of different drivers and cabs, even different cabs loaded with the same driver, and when you mix and match them the results are at best unpredictable, the worst case being the cabs will detract from each other as much as they augment each other. So if you must take on item from column A and one from column B do so it a Chinese restaurant, not a music store.
That's not to say that there isn't any benefit in using different size drivers together. There's a great deal of benefit in that when the drivers are dedicated woofers/midranges/tweeters with a crossover insuring that each operates only in their own bandwidth.
If this information isn't in the FAQs it should be.