To my mind OPEC probably has more to do with setting oil prices. They got PO'd at us back in the 70's & wrecked our economy with the Arab oil embargo. It could be argued that they wrecked it again not too long after we invaded Afghanistan.
They have a history of using oil as a weapon.
If you look at the member nations of OPEC you can see that many aren't / weren't friendly to American interests.
OPEC : Member Countries
One of the key member nations is Iran. Iran is more closely allied with Russia.
The theory that we are beating up on the Russians doesn't seem to hold. I don't think we exert that much influence over the market. The idea of global demand being off seems to make more sense.
If you take OPEC's mission statement at face value they may simply be trying to stabilize the global economy with fair prices.
OPEC : Our Mission
Now that we're mostly out of the Middle East they have no dispute with us. Better to get back to business as usual and stop making problems for the people who were making problems for them ?