Hello dr.j and welcome to cruise-chat;
very sorry to hear of your negative experience with Princess.
I can't for the life of me figure out why they routed you to Acapulco via Las Vegas and Atlanta. I have used Princess Air to almost every part of the globe Princess sails and never had an experience like yours. And the luggage--no surprise they lost it with a convoluted itinerary like that. I think I would have seen disaster coming and had my travel agent book the air independently.
As for Regal Princess itself, I pointed out it is an older ship and really can't be compared to the newer Grand class ships; it was built before many of the amenities on the newer ships were thought of. And it is not as elegant; but I was on her a couple of years ago and it was in no way sub-par to the newer ships--just different, and in some ways, better.
And yes, she is leaving the Princess fleet in September, but it is going to P&O. I have visited several P&O ships and I would say, if anything, they are better maintained than the Princess ships; so I doubt if P&O would take posession of an inferior product.
So I'm sorry you had a bad experience, but I believe your's was the exception, not the rule.