In my bedroom I have an old pair of ESS AMT1s with 10" drivers. The area of that cone is pretty close to the area of the 3 6.5" drivers in my Focal 936"s. The bass from the ESS is substantially inferior to the Focal. Likewise, when I bought my 936's I listened only to the 926 and 948 in the same room right next to each other. If the presumptions made about large drivers and large radiating areas being that much better we're true, I can't think of a better circumstance in which to observe it. Naturally the 928 kinda fell apart below 40Hz, but north of that there wasn't any lack of dynamics or power aside from the 948 being a little more sensitive. Beyond that, the 2 6.5" woofers in the Kanta 2 didn't pan out to sound or measure significantly inferior to speakers with larger drivers.
If my understanding of line array theory is right, the stack of 3 drivers in the Focals has the vertical directivity of a 20" woofer because of how they mechanically couple. Not that it's really significant since the start rolling off at 150Hz and are crossed over to the mid at 260Hz making their pass band wavelength much larger than 20". Even at 500Hz the wavelength would be a good bit larger than the cone of a 20" driver rendering it primarily omnidirectional.
I'm certainly not saying an array of drivers is cheaper than one big one, but some people out there are suggesting that. In my opinion it's a question of which technical challenges one wishes to take on. Making really stiff, light, well damped, large cones is a real challenge of one sort. Effectively integrating multiple drivers into a cabinet and keeping it price competitive is another kind of challenge. I don't find that dispersion or thermal effects to be real issues unless we're going to make the lopsided comparison of oranges to watermelons. In terms of area of cone moved, 3 smaller drivers will shed more heat and be more accurate than a 10" driver. It's the more expensive solution to the problem.
As for specific drivers, I wouldn't even know where to begin. I could only guess at what each of the 6.5" F cones in these Focals would cost if they sold them. $150-200 each? They sell the 10" F cone for $350 each. That kind of thing would blow your budget fast.