There must be a trick you've got that I don't because if I don't retrain, the AI is on my arse big time.

Ok the AI doesn't retrain but it has near limitless money and always stack away all the mercenaries. I just stopped an Arverni campaign in 266. Rome attacked me almost right away while I was stuck against the Aedui. I was lucky, I finished the Aedui quickly, I moved in Italy and in 4 turns I had 5 heroic victories... I razed Arretium and Arriminium, but even then, Rome sent stack after stack of mercenaries so I couldn't keep them. I must have destroyed over 60 000 mnai (and it's surely and understatement) worth of mercenaries, but I couldn't retrain my units fast enough to keep my advance. I had to cover a debt of -36000 and fight like a devil just to keep the damn Romies south of the Po. Since I was taxing like crazy just to keep my stack running, my towns stayed small. The last battle I fought, there was pedites against me. So the AI was able to buy off ALL mercenaries in Italy, because I couldn't buy any, AND was able to max his MIC. With 4 towns. This game was going nowhere. I was disgusted. I quit.

So hell yes I will retrain.

Unless somebody gives me his trick.