That's pretty much my point. Thank you for providing additional examples.
The FSF is in a unique position of power with respect to the GPL (at least the "ver X or later" variant). And because they ask you assign copyrights for anything you contribute to the FSF, they're in a unique position of power over that. Both give the FSF various (and differing) unilateral powers over your code, should you elect to extend those powers to the FSF. Those powers can be used in ways you do or do not agree with.
We trust that FSF won't disappoint us. They've earned a lot of trust from the community over the years, but that vague yet pervasive sense of trust is not a legal construct. As you say, "They have the ability; the only question is 'Will they?'"
The most likely answer is "They will not." But, it _is_ a potential single point of failure if I ever saw one...