I still don't hear anyone "proving" to me that TOS is all set in the same universe. The same circumstancial evidence used against STXI works the other way too.
Kirk's middle initial, Spock's uniform colour, the uniforms in general, the bridge crew and the Enterprise interior and exterior design are wrong in the "Where No Man..." universe.
Shuttles clearly don't exist in "The Enemy Within" universe.
Antimatter, in other Treks known as starship fuel, threatened to destroy the universe in "The Alternative Factor" universe.
TOS is 200 years ahead of today in the "Space Seed" universe, and 900 in "The Squire of Gothos" universe.
Lasers and Time Warp drive are on the Enterprise in "The Cage" universe.
Photon Torpedoes don't exist and phasers act like torpedoes in the "Balance of Terror" universe.
If all these obvious contradictions and altered premises can co-exist in the same universe, then it can easily
be that universe's Spock who falls though a black hole and watches Vulcan die in STXI.