My Private experience...

Use only one (two or three if required for the next generation) general to take all your fight... never let him command too numerous army... Letting them fought defensive battle on advantageous ground is pointless, use captains to do that... Try to get Alexander-styled offensive

In my Romani campaign, I group one of my young, and military talented general with 1 equites romani, 2 hastati, 4 rorarii, and 2 acensii. If you need large stack of army, let a great army of captain walk behind them with some quality troops, but only group them as one when you really need it to win (not to merely overpower without thinking)... Another factions may well use low class troops, and get outnumbered everytime you fight... note that I use medium battle difficulty, with hard campaign...

Put them as a suicidal (but not a certain suicide) attack force deep into enemy territory and wreak havoc, ambush and capture their towns.... at least you will got high starred general, with poor to non existent influence and managements...