You are on the right track.
But think in terms of one sub cone to one high cone.
Each octave reduction in frequency requires four times the air displacement to equal the same SPL (sound pressure level) , while at the same time our ears are far less sensitive to low frequencies.
If you don’t have large cones, or small cones capable of a long stroke (displacement) your subs will run out of gas way before the tops, regardless of how much power put in.
A “bigger paddle” does not have to move as far to move the same amount of air as a small one.
But a “bigger paddle” requires more energy to move.
Horn loading can reduce excursion by coupling a bigger slug of air to a smaller throat.
Most PA HF is horn loaded, but as you go down in frequency, horn size must increase, requiring rather large horns (or multiple long, smaller horns) for LF.
Tom Danley’s tapped LF horns cheat this requirement a bit, but there is no way around it, low and loud takes up space.
Displacement applies to high frequency diaphragms as well as LF or MF.
One problem in comparing HF compression drivers is there are two dimensions to consider, exit diameter, usually 1, 1.4, 1.5, and 2 inch, then diaphragm size, ranging from 1 inch up to 4 inches.
Then of course, the horn the driver is coupled to makes a big difference.
As for dispersion, 90 degree is a good compromise for most rooms with one speaker per side.
Art Welter