The flaw is that some players grow WAY faster than others, so a player could have a ton(for the beginning) of ALU ready before they're out of BP. They could attack a player who grows slower and wipe him, and that player may not have enough defense built yet because he isn't large enough. I hope you followed that.
I know the game is the survival of the fittest, but it's kinda a coward move to attack somebody while you can't be attacked.