Aye - each of us should play the way we get more fun. I tend to be more mechanical because I'm playing a computer AI. If I know there is a tactical or strategic weakness I exploit it - whatever units I or they have. The fact is there is no way to have a perfect game. You may have a superb plan that ends up with your cities earning efficiently and armies that are perfectly balanced - then a boatload of Carthaginians lands on Sycily out of the blue. Personally I'd enjoy that, but you can forget your perfect plan.
I know I can beat all the units in the game. Cretan archers will lose to a flank attack by heavy cavalry. Sarmatians can be wiped out with a couple of Rhodian slinger units (we know mercenaries will rout early). I remember outside a city killing two elephant units by repeated cavalry attack. My main approach is to check the unit attributes and if they are much better on defence or attack that's how I use them. For instance a phalanx is significantly better in defence so I rarely attack with them (has to be done if the AI is hanging back).
I like the historical aspect. I think TV programs used this game for simulations when it first came out. The game is very educational but I find it difficult to mimic actual events. For instance Caesar with a smaller army beat Pompey by taking one in three men from his front line and concealing them on the flank to combat a cavalry attack he knew was about to happen. Can't do that in this game.
Poor mercenaries I use as cannon fodder and sacrificial goats when my army is weak.