Wich aircraft would be able to climb higher in this case? For sure not the A321ceo. Climbing up to flightlevel 370 or 390 with the A321neo close to max TOW was the norm, whilst the old 321ceo would have been stuck at 310 or maybe 330 all the way.
Even that depends. The A321 CEO with sharklets can climb higher than the one without, around 2 to 4k higher initial cruise.