You made a common error amongst miniature war game players: you fight according to the rules, not to the historical situation. I've played a lot of Napoleonic miniature games, where cossacks - due to the rules - were almost invincible. In real life they were good, but definitely not supermen. Otherwise every army would have had cossack units. 

Some players learned the rules by heart and build an army to make the most out of it. Often they would win, but not because their army was historically better managed, but because they build an army that would work best with that particular rule set. That very same army could be trashed with a different rule set where other units had different/better advantages. 

The Romans were very pragmatic. Whatever worked, they used. If something didn't work anymore, they tossed it away. The Romans used the checkerboard formation ... because it worked well for them. Very well. 

There isn't a a game that simulates combat 100% accurate. It's always a toss up between realism and playability. You can add some extra realism to any game, be it a board game or a computer game: 

First march 20-40 km in full gear. Then do 20-40 push ups followed by a 100 meter dash, again with full gear. Ask your friends to paddle you with sticks while you have to play the game with a specific short time limit to make your decisions. -- And even that is not real combat. ;-)

In the army we had to do just that to qualify for a shooting badge. Minus the paddling, of course. Shooting a pistol a 25 meter on 5 targets is not very difficult. But it is with the above extras. It was still a heck of a lot easier then real combat as the targets didn't shoot back.