The maps certainly need to be examined individually. It's always unfair to make global judgements from single examples.
I think adjusting the ladder points according to the number of turns required to win will suffice. If you win in under 10 turns, you should get no points, or nearly none. That will prevent the objectionable behavior. However, it might lead to some other abuse if the only factor is time. That is why I suggested a system in which points are awarded based on map size, then scaled according to the amount of turns required to win.
50x50: max 10 points, 1-5 turns multiplier of zero (drops should not give any ladder points), 6-10 turns multiplier of 0.5, etc.
It's a crude example, so don't get hung up on the specifics. The numbers would need to be carefully analyzed and balanced before implementation.