I just picked this up today, so I do not have first hand knowledge of this particular game, however in some older PC RTS's I have played, when you start, you always choose how to divide and use your resources.
Sounds like the main strategy is to focus all of the starting resources at their disposal on troop production, and nothing else. My guess is if you were to ward off that first attack, you could launch an immediate counter-attack and find their base in exacly the same state it was when the game started, with nothing built up whatso-ever.
Also, with the initial resources depleted by the initial push to create the attacking army, chances are you could take a smaller force and stand a good chance of a successful counter attack.
This is probably a short lived strategy that will not stand the test of time, and more importantly, the test of players who know how to counter it.
My thought would be to create a full army of archer's in anticipation to this initial attack, and once in range, focus all fire on one enemy until dead, rinse and repeat. Chances are, the opponent is creating them and sending them as fast as possible, so you will be able to decimate the army with very little losses as he will probably not stop and gather a mass of forces large enough to push through the hail of arrows falling on his head.
But, like I said I haven't played this particular RTS yet (tonight
YES) so I am sure it might be more complicated than that.