It's only a question of what defines the "balanced gaming range" in any game. Heroes ALWAYS has been that way that some features were unbalanced depending on the scope of a map - actually I remember maps CENTERED around exploiting an unbalance to create something outstanding.
Now, that's ok for SINGLE player, but definitely not for MULTIplayer, I suppose we agree here.
The thing is now, if you make an MP map you have to have a clear grasp of the range the game as such ill be balanced between two factions.
For example, it is IMMEDIATELY clear for HoMM 5 that once a map becomes too rich in terms of money and resources Haven and Academy will have an advantage, since they can put excess m&r into a direct improvement of their armies,
Hit&Run is eomething not limited to Dungeon, mind you: it's just that Dungeon heroes and Dungeon creatures work best.
The trouble here is, though, that this simply reduces this what I would call "valid map range". MP maps simply shouldn't allow heroes levelling up too much. If maps are geared to max a hero out between levels 15-22 or something like that, and you keep money and resources what I would call in check, this is not a problem, because the Mentoring skill and the money necessary to buy half a dozen heroes is not somthing you can do IN EXCESS then.
So my advice would be this: instead of banning or outlawing all kinds of perfectly valid behaviour map makers should simply made sure to keep their maps in a range that doesn't make those things necessary which needs discipline when you make them.