I think it's definitely a factor. As a corrolary, because Southwest uses their gates more efficiently, there usually isn't an empty nearby gate where you can sit if the waiting area for your gate overflows. On legacy airlines, there's usually an empty gate area somewhere nearby. (Good for the customer, bad for the airline...)

However, the overriding factor in the perception is the boarding chutes/lines, and it always will be until Southwest gets rid of them.