What goes wrong with these tactics (which seem good) when you use arbalesters?

I like the arbs myself. Defensively I use a large amount of them (up to half my force, or more if I can keep them as reinforcements) up a hill, hidden behind spears or chiv. serg. - they tear large holes in enemy units, especially those damn camels. Offensively I'm moving away from taking archers at all in favour of light/medium infantry. However your tactics seem interesting (no shock troops?) and I'm gonna give them a try 'cos doing different stuff is fun!