Strategic importance of Turkey.
What about the US ? Incirlik is one of the important airbases for them.
You have obviously not been to the region often.
The US has a large airbase in eastern Turkey, Incirlik, but the Americans are widely despised and mocked among the locals for being there. Everyone knows that the only reason the base is there is because the US pays $2 billion a year for it to be there, and most of that goes directly into the pocket of King Erdogan. And King Erdogan uses this money to build his new royal palace in Constantinople, and to 'persuade' the more gullible sharia electorate in the east to vote for him. Nice little freebies are on offer, like free fridges, free coal and free potatoes - just what the rural unwashed want.
So Incirlik is a nice little earner that keeps King Erdogan in power, no more, no less. As their special book says: "you can enter into an aliance with the non believers if you are not in a position of strength, but it can be broken after ten years or when the situation changes". King Erdogan observed something similar when he said: "Democracy is like a train. You can get on an off it whenever you want.". Anyone who fully trusts King Erdogan needs to think again. The Americans know this, or should know this, and have plans to relocate to Cyprus at short notice.
As to the Russians needing oil from the Black Sea, that is not true. While Syria is not exactly overflowing with oil, it has enough to supply Russian needs, both in the port and the airbase near Latakia. The oil fields south of Homs are still in government hands, and still working, although at a reduced output. So Russia has no immediate worries about oil supplies to its forces.
As to Turkey controlling the Bosphorus, that may be a bit of a worry for Russia. Would they have to force their way though? Not yet a while. They have enough ships in the Black Sea (taken from Ukraine) and Med not to worry at present, and they can always bolster the Mediteranean fleet via Gibraltar. That is something to think about many moons from now. So does Russia have any worries about the strength of their position in the region? None at all.
ST