The problem is new players are not 'quarantined' to the the tutorial map but instead can chose any map to start on. Usually this would only be those who know what they are doing (i.e. a player leveling up a new acct to use as a multi) They often use the bonus troops to help their main account in other maps.
If every new player was forced to play the tutorial with their bonus troops and if they instead chose a different map they should then start with a normal set up.
This does not disadvantage the new player, they can play the tutorial map with the bonus and learn the game and all other players who start one of these maps know that any first timers will have that advantage.