Same with gas. The qualities are not the same. For example from what I gather the US gas is among the lowest quality gases alongside UK gas. So even when they import some LNG from US it still is low quality. Not to mention that US already significantly reduced its LNG export after the fake explosion in their LNG facilities.
Yup, they can always do more to refine or further improve but that's additional cost in the short term (building secondary refineries, e.g.). Though that also does mean it is about affordability in the long term.
I sense some changes coming in sanctioned oil (Iran as you mentioned, Venezuela possibly).