IMO, it doesn't matter what any of us think is what you should receive, it only matters how much you think your disappointment is worth.
I understand your displeasure and am sorry this happened to you. "Ship" happens in life.
HAL's Agent, your Agent, someone messed up. Okay, they have made it better.
Why did it take your TA so long to discover this error? Did you advise your TA you were having trouble booking excursions, that your reservation was not showing up? Did you let it 'ride' for too long without speaking up? Had you inquired about the problem earlier, that cabin might have still been available. I am not blaming you for the error but just mentioning this in the hopes we all can learn we need to take initiative if we think our reservation may have a glitch.
You still have the cruise you want and are in a more costly cabin.
Being lower on the ship is the preference of many people. They say the 'best ride' is in the middle..... half way up and in the center.
I hope you can move along and start looking forward to a fabulous cruise.