Nope. Actually, the AE210's have essentially identical air volume per driver as the AE410. There's just more hieght, so there has to be less depth. The diff is literally negligible.
Nope. While they are shallower, stability is simply not a problem at all.
True.
Very true. It's definitely a negative to transport two 40 pound packages vs one 65 pound package, and the compactness of the AE410 accentuates the convenience.
Here's the thing. From a tonal standpoint, the 410 is going to probably have a slight "coherency" benefit simply because the drivers are grouped closer together and it's tuned as a 410. There are also cost and portability benefits. If you were always going to use/need all four 10's, the AE410 is the only sensible choice. Period.
HOWEVER, if modularity is very important to you, and you would often enough only want/need a single 210 cab, but also want/need 4 10's often enough, and the price difference was not a problem for you, the 2x210 makes a lot of sense. It's going to be a slightly "bigger" sounding rig due to the spreading of the drivers, and you'll also have a bit of a self-monitoring benefit with the added height on smaller stages. From a portability standpoint, there MIGHT be an advantage in some specific cases where your vehicle can't do the larger 410 cab, but could do two smaller 210 cabs.
IMHO.