Your not in a minority, I think a lot of our support dont rate either of them. Personally, I dont think either are great. But they are a long way from the worst we have ever had. McGinley is a better defender, but cant cross the ball. Carroll has much better delivery but consistently gets caught out of position and cant block a cross. In short, roll the 2 into one and you might have a player. Unfortunately that player would be off to pastures new within a season of their arrival.
Its where we are as a club in the modern game and why context is always required when assessing our players.
I dont think GA will be looking for another left back, but I wouldnt be averse to someone coming in if one of the above can be moved on.