The more open it is the more it can be exploited. As you get the economy down the only thing left to do is PvP. You don't fight for resources anymore. In fact the veterans will pay you after the fight for your losses. Decent ones at least.
There are other players out there that are at this point and are bored with the game. So they find it entertaining to set up armies that are not intended to be made and destroy certain people.
A great example was the wizard I said. That guy killed 42 units of a new player before he could even get to the single mage. He created a 1 unit elite army to hunt new players. He was level 100 most likely and the spell he used is getting nerfed with 24 hours. But the more open you make the practice match the more ways people will find to exploit it.
So we want to prevent these type of things from happening. I know it sounds fun playing elite units but they are for specific roles and wont help until a new player understands the basics. And once you have the basics down the learning curve is not hard to understand with these units. So lets keep things less complicated which will actually help new players learn the game faster.
But then again, we all have our opinions. And this is just for discussion. The Devs are the deciding factor on weather there will even be a newbie matchmaking system.