Well, first, sending the archers as 1st wave isn't a very good idea
They should sit on a flank (NOT directly behind the shock troops !!
) and be ordered to fire.
As for the hvy cav/knights, it depends : what nation did you play ? Ulm knights are quite trustworthy, Arco "hvy cav" isn't ...
And how many Groups did you had ? 1 only group can rout if its sole leader get killed ! Spread the troops into several, such as :
R Wing : 15 archers, fire closest
R Centre : 25 cav, attack closest
L Centre : 25 cav, hold and attack
L Wing : 15 archers, fire archers
Normally you should have won with the archers alone... the 1st cav wave then would have mopped up the routers. If ever it didn't work there was the 2nd wave.
But maybe a strike of bad luck struck you !