Well, yes. 16 dBi gain is only on the highest channels no longer in use. Which was my point.
If you scale up the antenna, you'd increase its dimensions horizontally, vertically, and in depth. Increasing the vertical dimension would increase the separation between the three sets of directors, so they would no longer overlap so completely at the channels still in use. You'd have to make it 30% larger in every dimension to get that benefit though. That's a lot more metal - if you increase all dimensions by 30%, including thickness, it's more than double - but you could probably eliminate the middle Yagi entirely, clawing back 1/3 of the cost without losing much gain.
That still makes it 50% more expensive, and I don't know if anyone has analyzed that modification.
I'm unsure of the benefit of slightly wider vertical vs. horizontal beam width. It could be useful in certain situations, but YMMV.