The resource drain % is not changed with the new quality scaling

Yeah, I opted to just leave that alone because it already feels like overkill most of the time to cut it down to a sixth by the time you get to legendary, especially since you tend to have a lot of mining productivity boost by that point, and the standard progression isn't really clear about where it would go from there, since it's 5/6, 4/6, 3/6 and 1/6 for the default levels. I guess I could change it if there's a demand for it because the difference feels minor either way.

I wasn't sure if it was intentional or an oversight since everything else seemed to be scaled

I'll argue that:

1. Legendary big mining drill in vanilla is already very OP
2. Having the drain reduction unaffected by this mod feels unsatisfying.

So my suggestion is:

Add an option to lower the drain reduction of mining drills (big and small) to 4% per quality level, and use the mod's levels.

So for big mining drill it will be 50%, 46%, 38%, 26%, 10%.

For legendary this is similar to vanillia, but slightly weaker. And the progression from common to legendary is on par with other things in this mod.