@ghdprentice You are certainly correct in saying that bass speaker engineering has improved greatly in the last 20 or 30 years. But that would be a reason for building larger bass speakers, not smaller.
In principle, leaving aside engineering issues, a big unit will deliver more bass than a smaller one. This is why in earlier times 12 inch units were commonplace although as you say 'boomy' - read 'distorted'.
But there are engineering reasons why two smaller bass drivers work better than one big one. I bought KEF 801s when they were launched. These had a single bass driver of 15 inches. But a few years after KEF launched the 802 with two 12 inch units and not so long after that they discontinued the 801.
As you say, to obtain quality bass you need high driver throw, speed and accuracy. This is mainly achieved by minimising the mass of the cone and other moving parts whilst maximising its stiffness. This latter is crucial as flexure will create distortion, It is axiomatic that, all other things being equal, this is more easily achieved in a smaller diameter unit. Indeed I suspect the flexure of the cone increases as the square of its diameter.
By the way, you say your 8 inch units 'go down' to 24Hz. But what is the output down there relative to the mid-range? I'll warrant it's at least 10dB down.