Those who have not yet been affected by a propulsion problem on the Millennium, Infinity or Summit are indeed fortunate. Granted, most who sail these ships have not been affected, but at the end of the day tens of thousands have been impacted by this problem. There is just no getting around the facts and while I can appreciate champions of Celebrity, who have not been affected, in trying to minimize this problem, the facts are still the facts.
While it certainly is a "happy" thought about an extended cruise, but the fact is that no Celebrity cruise has been "extended by a day or two", but many itineraries have been cut short by this problem. Even if cruises were extended, wouldn't that mean someone else's cruise would be cut short by 1 or 2 days?
Saying the Celebrity mclass ships are still premium or not, is still just a matter of opinion and that is all. As I said before IMHO, I would not consider any cruise ship to be premium that has a design fault that has had such a long history of problems. Others can certainly have other opinions, but at least mine are backed up with facts and experience as to what can happen on these ships.