Personally I really like the Refineries as they are. I've never really had a shortage of oil tbh, it's one of the resources I don't worry about as much.
And I think requiring the knight to have two different strategics and being stronger as a result is a bit overkill? Like, requiring two resources to build seems silly, it would be the only unit in the game to do that lol. And for it to be strong enough to be worthwhile it would effectively dominate the era if you did have those resources. Seems like it would mess up the balance we have currently have IMO.