Sure, Wawa's in Andy's league in two regards - number of slams won + winning the DC (which I don't consider that important tbh)
Andy's not in the league of the Big 3 in terms of slams won nor weeks at no. 1, but he's in their league in pretty much every other regard.
See above.
Essentially, Murray's in a league of his own. He's obviously not at Big 3 level, hence the 3 slams. But he's obviously not on a rest of the tour level either, hence his 40+ tour titles, relatively decent h2h vs. the Big 3, 14 Masters, 12 slam finals and now snatching the no. 1 ranking away from a Djokovic who's won 2 slams and 4 Masters this year + made the final of another slam and the WTF.
Until Wawa, there was no one else anywhere near Murray in terms of career accomplishments outside the Big 3. Now because Wawa has gone all Stanimal 3 times in the slams, he's ended up with as many as Murray despite only playing 1/4 of the slam finals to do so.
Wawa is a personal favorite of mine, Murray isn't.
Yet I have no problem putting Murray in the Big 4 category. Why? Because he's been an essential part of the conversation for the past 9 years, being at the business end of most big tournaments time and time again, rarely dropping below 6.000-7.000 ranking points – a number neither Wawa nor Delpo or Söderling have been above iirc.
Wawa's done that for 3 years now and only in the slams + WTF (minus this year for the WTF).
Does that mean Murray is as good as the Big 3? No. But he doesn't need to be to be part of their group. Djokovic wasn't either in 2010. And Rafa was 10 slams behind Fed in early 2010, but leading the h2h.