I do agree, Turnabout Intruder
isn't the same kind of narrative ("closing the book", as they say) as the others. It isn't a fair comparison, but it is
TOS's finale, for better or worse. Personally I've come around to thinking of TAS as an extension of TOS... and therefore, I tend to think of The Counter-Clock Incident
as being TOS's 'true' finale. It feels a lot more like one too, what with the Enterprise's very first captain coming back for a visit and all. Makes for a much more satisfying ending.