Limitations are obvious -- slow, can't shoot, weak against foot.
Shattered by mounted seems like a limitation, but it really isn't, because you can use that to make the enemy get stupid. They are surprisingly good against mounted. And to quote the Russians, sometimes quantity has a quality of its own. Fighting mounted they usually have numbers (which means overlaps) and you can afford to lose 2-to-1 without really worrying about it. More than that -- on a flank where the enemy is attacking with mounted, a wall of Bow Levy serves as a combination of obstacle, glistening plum, and pip sink for the enemy.
You have to understand what a wall of Bow Levy can do, and cannot. They cannot fight in the open against close-order foot, although they will often survive that for quite a while. They cannot deal with Cataphracts, although they can often do well enough against Knights or Elephants. Javelin Cavalry are pretty dicey, but they do fine against Chariots, Bad Horse, and Battle Taxi. I had a hilarious game against Jack Sheriff once, my Neo Babylonians vs. his Later Sargonid Neo Assyrians. He charged his Chariots into my Bow Levy wall. On the face of it, it looks like a reasonable idea because the Chariots shatter any foot. I lost a bow levy, I think, but Jack took his survivors out of there weeping, swearing never to try that again. I called it the "Comfy Pillow" defense, where the Bow Levy seem like such a great place to attack -- until you do, and you realize how desperate it is when you have an overlapped Chariot fighting a Bow levy, at +1 to +3. Shatter don't mean much then, and I had the numbers for a double line of Bow Levy across the map, more or less.
The big thing is not to have a single line of Bow Levy. A double line is fine; you can get half again as much width with alternating single/double/single/double formation. Or at more risk, a 3-1 formation (3 front line guys with one guy in reserve behind the middle one).
With a big Bow Levy army (say Neo-Bab 15) Bow Levy, that gets you 7 frontages as a double line. 10 frontages as a 2-1, and like 12 as a 3-1.
The best part, if it works, is that the Bow Levy army absorbs the enemy's pips. They have to commit forces and pips to attack a part of the battlefield where you do not have to commit pips. This gives you a powerful pip advantage on the other flank.
The hardest part is making it work -- forecasting where the enemy will be, or making him be there, so you will have your formation there in advance. In many ways this is like Artillery -- it only works if you can figure out, three turns or more in advance, where the battle will be fought. If you DO figure it out, it's very powerful -- but if you don't, quite weak.
Which makes the glistening plum aspect important. Bow Levy look so inviting, and so vulnerable to mounted, that the enemy almost can't avoid staring at them and imagining what will happen when his mounted hit that vulnerable line. Since you are nearly never going to be able to advance them anywhere useful, you've got to use that. (About advancing them somewhere useful -- march moves on the first turn, if you have the command points, can get the Bow Levy into some useful places. Just make sure to have strong flank protection with terrain if you are fighting, well, anything -- nothing sadder than a bow levy line that has been turned and is being eaten from the flank)
Plus, with some opponents, the social aspect. You can mock them for being scared of Bow Levy. They will never live it down.
Bow Levy are too numerous (and therefore use too many pips) to be much use offensively in difficult terrain. They are fine there on defense against anything but Raiders. But difficult terrain on the edges of their broad open-terrain line is wonderful, because you can go single-deep there.
Small groups of Bow Levy (in an army with 3-4 stands of them) are even more useful than big ones. They are wonderful for flank protection. Which mostly puts them up against mounted, which is what they want. Enemy mounted will often threaten a flank; a foot army will often be forced to respect that and station some dudes down there. But those are wasted troops if the enemy doesn't attack there. Best is to make those troops as cheap as possible, so you have more strength of the army to put other places.
Another thing: Bow Levy are open order. That means that you can have an Open Order reserve of a stand or two ready to move THROUGH them. A single JavCav to fill gaps against a Knight charge, or to move through and hit a stand in the flank. A single Knight or Chariot to fill gaps against enemy that are putting a wall of foot into your wall of Bow Levy in the open. The timing needs to be careful, of course -- you have to virtually guarantee a kill -- but still a good gig if you have to use a big wall of bow levy in the open against some other troop type.
In summary, Bow Levy en masse are not an offensive weapon -- but they can be a good counterpunch weapon. And Bow Levy in groups of 3-4 are wonderful for a foot army fighting a mounted army, or the mounted component of a combined-arms army. There are often a thousand places to put them to use.
