It is perfectly possible to have an excellent cruise on an MSC ship when not in YC. I've done so, many times.
It's a forum for people to post opinions and that's yours. However, it's an inaccurate assessment to say anything other than YC is "crap". Borne out by myself, others here who review and according to the many thousands who choose other categories to sail.
Is YC wonderful, yes, it is. Is everything else, as you've described it "crap". No, it most certainly isn't.
I find it quite a disrespectful attitude to those who've booked their trips outside of YC, to state their cruise will be terrible because they're not YC. People save and sacrifice to book cruises and to disregard their experience isn't kind or true.