The A321LR has 30% less passenger capacity than the 767-300ER when configured with comparable cabin standards.
It also has 1,500nm less range than the 767-300ER.
The operating costs on a trip and seat-mile basis are considerably lower, however.
If the majority of planned routes are within the capability of the A321LR and other aircraft, with longer range, could complement it on the longest routes, it is a more economical alternative to a new 767, both on a Cash Operating Cost basis and when including capital costs.
This assumes increased route frequency can compensate the higher capacity of the 767.