You write "Of course you cant avoid completely [that the skypriority lines are slower]".
I disagree. It is of course >99% avoidable, but could be quite expensive.
Actually you agree with me, even if it is avoidable in 99%, you still can't completely avoid it, in some airports it is handled better, in some less, either way it is not controlled by the airline.
I believe that at a specific airport, there is (was?) general feeling that skyPriority can be slower. If this is real and consistent, it would then mean that the advertisement is false or misleading.
So should they remove the advertisement because in one airport (out of probably few hundreds?) passengers have a
general feeling (not even backed up by hard data) that it is always slower?