On paper this sounds like you should never have beem denied doc. However there are a couple of details that sound off:

-You said you were in the SECOND bus? Knowing that your flight had a delay and that you were on a short connection, the crew should have briefed you in advance and you should have been whisked to the front for the first bus. How did that not happen?

-You said you waited 10mns for the "express lane". There is no express lane. Did you mean the short connection lane? How come it took so long was it a day with may delays?

Seems strange that you allowed yourself to wait for 10mns and for a 2nd bus when you knew you were down to the wire.

P.S. I made a NS to S connection yesterday in under 12mns.