Well, Murray beat peak Wawrinka at Roland Garros, where Stan was defending champion and then beat him again at the WTF in straights. They last met at 2017 RG where they fought a 5 setter which Wawrinka edged. Murray was already feeling the effects of his bad hip by then and Stan got injured too.
Stan does have a winning record vs Murray overall on clay (tied at the French though) and at the U.S Open. Clay isnt really surprising to anyone of course, but the U.S Open is surprising to me since a)Murray career wise is significantly better on all faster surfaces, b) even moreso 2 of their 3 matches there were before Wawrinka was even any semblance of a top player. Remember those first 2 matches occured in 2008 (won by Murray) and 2010 (won by Wawrinka). Even the 2013 U.S open quarterfinal match was before Wawrinka had ever won a slam, before his first slam semi I believe, since that occured at this very U.S Open. I dont believe they ever played at the Australian Open which is Stan's 2nd best slam, maybe they had a meeting many years ago I dont know about.
Murray can hold his own for sure, even beating prime Wawrinka on clay is evidence of that, but it seems Wawrinka is definitely a tough opponent for him. Their head to head is almost a tie, something like 11-9 or 11-10 isnt it? I guess that shouldnt be surprising when both are 3 slam winners, but somehow it feels like it is; maybe because of how useless Wawrinka is against Fedal, and how extremely lopsided his overall losing record is vs Djokovic despite the slam success. And that is counting all the matches for many years when Wawrinka was a journeyman regular top 20 type player, which probably takes up about half those matches, and he still managed to make it a very close head to head.
So breaking down the Big 4 members I would say Wawrinka is just a simple asswipe for Fedal, with even grandpa Fed barely breaking a sweat to beat him off of clay and slow high bouncing hard court, a legit threat to Djokovic, and an even bigger threat/quite competive nice rivalry for Murray. In addition to Federer being a horrible technical match up for Stan (and the much better player), Stan seems completely spooked and timid when they play ever since I first saw them play one another in 2008, probably the dual Swiss and being in Federer's shadow at home thing. By contrast Del Potro is a tougher opponent for Fedal than he is for either Djokovic or Murray, especialy Djokovic who is his nightmare, especialy in a best of 5.
