Who robbed my Dukedom

The Royal Hospital was built by the Duke or Ormond, a fact testified in stone and plaster by his coat of arms found above its north Door. But look closely at the crown on top of the arms: its not a Duke's crown - its that of a Marquess. Now (as everyone knows) a Marquess is an important title - but its not quite as important as a Duke. How can this be?

The Duke was made Duke in 1661, the hospital was commenced in 1680. Why didn't the Duke claim the title he was entitled (no pun) to? It would seem that the Duke got made Duke twice. His first dukedom was indeed in 1661 in the IRISH peerage. He didn't get made Duke in the English peerage until 1682. I appears James (as he was known to his friends) felt that a mere Marquisate in the English peerage was better than a whole Dukedom in the Irish. What a cheek!!!