Russia is also not the Threat it was. It still has vast nuclear weaponry. You could argue that having a nuclear threat based in the black sea could prove useful, but would you really want your best technological advantage in such a precarious position. It would take very little to blockade and trap a sub in the black sea. We also have a credible land link to the black sea now.

So yes, this would be true back in the 50's when Turkey was invited. It is not so much the case now. Military transport is vastly more refined. Even the political landscape around Russia has turned on its head. Turkey's significance is diminished many fold because of this.