There’s nothing about AB testing that requires you to use short-term metrics. I used to manage AB tests for online dating sites (OkCupid, Grindr) where subscription revenue is what matters, and the gains of any strategy will take months to materialize. We were well aware that, say, raising prices would yield more short-term revenue at the expense of long-term revenue. That didn’t stop us from testing, it just made the statistics more complicated.