I think there are some misconceptions here. Broadly I think some assumptions being made above (CX is killing J capacity) are incorrect.

Aria 77Ws is not a material fleetwide reduction in J. The 77Ks will go under the knife. They have 40 J. Aria has 45. Each 77K to Aria conversion will add 5 J seats. 77A has 53 so it's that bird which loses 8 each. But seriously, we are splitting hairs here.

In terms of what's premium and what's not. I am fully removing my sentiment and my own personal preferences. (To be candid: I don't really fly PEY or Y at all.) But, I am speaking to the market at large. The reality is PEY is a premium offering. It is 8 abreast in the 777 and A350, vs 10 and 9 respectively in Y. The pitch is significantly greater.

It isn't too long ago when J seats didn't look too different from today's PEY. Setting aside romance of the sky nostalgia, on a real estate basis - the only metric that really matters in dollars and cents terms - today's PEY footprint is not vastly different from the early business class layouts or what used to be called (a long long time ago) 2nd class. That I don't care for the product myself as a customer, doesn't deny there is a very large traveling public who vote with their wallets.

Either way, it doesn't matter too much if we are to call it premium, or "enhanced" economy, or whatever. The reality of the airline industry in the last 10-15 years is this is a highly purchased product with significant demand that has provided the only real secular (non cyclical) demand growth in the same period, and airlines ignore it at their own peril. Business class demand goes in cycles. The growth of PEY from zero 20 years ago to a significant footprint on every major airline today, is a market trend that airline bean counters are forced to reckon with.

Personally, and this is only my speculation, but I think the gulf between J and Y is now massive (wonderfully evolved flat beds in J, same ole pain in Y) that it's quite obvious a class in between (old 2nd class = today's PEY) rises up to fill the gap.

As for Aria itself, I too am disappointed by it. A basic evolution at best. With a very flimsy armrest.