TL;DR
Pumpjacks, like mining drills, gain reduced resource drain with quality. But oil wells, unlike ore patches, don't run out.What?
Like mining drills, quality pumpjacks gain a reduced resource drain. However, where this is very valuable with mining drills - a 66% resource drain means you can extract 50% more ore from a given resource patch before it runs dry - oil wells are infinite (as are sulfuric acid geysers and fluorine vents). Fresh wells do produce oil faster, and technically a higher-quality pumpjack will cause them to deplete more slowly, but once they hit their minimum output of 20% of what they started as, a quality pumpjack provides no benefit at all. (Note that this doesn't apply to lithium vents, which contain a finite amount of lithium brine and deplete like ore patches.)To compensate, I propose that quality pumpjacks be given a buff to their output rate. The simplest solution would be to just give them a straight quality-based multiplier to their output rate, same as production buildings like assemblers. A more balanced solution, however, might be to make it a buff to the minimum output rate; thus e.g. while a normal pumpjack on a fully depleted oil well will produce 20% of what it initially output, a legendary pumpjack will never drop below 50% of the initial output.
Note that in either case, the reduced resource drain should still exist, at least in the case of lithium brine.