Tuning and notation are orthogonal. The major scale can be played with many different tuning systems. If you do want to talk about just equal temperament tuning in this concept, the point of equal temperament was to smooth out the spaces between notes for better handling of musical ideas like modulation. Even with that the 5th can still be seen as 3/2 even thought it's approximate. The 2 cent difference is well within the just noticeable difference .