On the contrary, only if you think it is all about the Slams. I (and others) think other aspects need to be taken into account. Unlike Wawrinka, Murray has been ranked world #1 (the only active player to be so other than the Big 3) and has won many more titles (46 > 16) including big ones (20 > 4) than has Wawrinka. In these respects he is much closer to the Big 3 than he is to Wawrinka and that amply justifies regarding him as a member of an exclusive group with the Big 3. Wawrinka can certainly be included as a member of a Big 5 but none of these groups are mutually exclusive.
You sure? Murray is closer to Wawrinka than the Big 3 in 5 categories (Slams, overall titles, weeks as #1, Year End #1, Masters 1000), while he is only closer to the Big 3 in 2 categories (Olympics, ATP finals).
Slams: Murray is closer to Wawrinka than he is to the Big 3 in Slams, as there are 13 Slams of difference between Murray and Djokovic, while there are 0 Slams of diffrence between Murray and Wawrinka.
Titles: Murray is closer to Wawrinka than he is to the Big 3 in titles, as there are 31 titles of difference between Murray and Djokovic, while there are 30 titles of difference between Murray and Wawrinka.
Weeks as #1:
Murray 41
Rest of the Big 3: 208+
Wawrinka 0
Calculus of the difference:
208-41 = 167
41-0 = 41
Murray is closer to Wawrinka in weeks as #1 than he is to the Big 3, as there are 167 weeks as #1 of difference between Murray and the big 3, while there are 41 weeks as #1 of difference between Murray and Wawrinka.
Year End #1:
Murray 1
Rest of the Big 3: 5
Wawirnka: 0
Calculus of the difference:
5-1 = 4
1-0 = 1
Murray is closer to Wawrinka in number of Year End #1 than he is to the Big 3, as there are 4 Year End #1 of difference between Murray and the Big 3, while there is only 1 Year End #1 of difference between Murray and Wawrinka.
Masters 1000:
Murray 14
Rest of the Big 3: 28+
Wawrinka 1
Calculus of the difference:
28-14 = 14
14 -1 = 13
Murray is closer to Wawrinka in number of Masters 1000 than he is to the Big 3, as there are 14 Masters 1000 of difference between Murray and the Big 3, while there are 13 Masters 1000 of difference between Murray and Wawrinka.
Olympics:
Murray 2
Rest of the Big 3: 0-1
Wawrinka
Murray is closer to the Big 3 than he is to Wawrinka in this stat.
ATP finals:
Murray 1
Rest of the Big 3: 0-6
Wawrinka: 0
Murray is closer to the Big 3 than he is to Wawrinka in this stat.