Let's take a look at top 5 wins at AO + USO (HC slams)
Stan Wawrinka is 9-10 vs top 5 in HC slams.
Andy Murray is mere 4-11
Stan beat Berdych once, Murray twice, Nole thrice, Nadal Nishikori and Medvedev once.
Andy beat Nole once, Nadal twice and Federer once.
Both Stan and Andy beat Nadal who was unfit. But Stan beat Nole who is the HC GOAT 2 times when fit and Andy did it once. If both played each other, and both are fit, money will be on Wawrinka.
Delpo is 4-7 vs top 5 in HC slams. He beat Roger 2 times and Rafa 2 times. Rafa was unfit once and Roger once.
Even Cilic is 4-10 vs top 5 in HC slams. Beating Murray once, Delpo, Fed and Nadal (unfit).
Kei Nishikori is 4-8 vs top 5 in HC slams. Beating Nole Andy Wawrinka and Ferrer. No one was unfit.
So Murray has as many HC grand slam match wins vs top 5 as Delpo Cilic Nishikori. But they all lost less times vs top 5 than Murray.
Stan has double the number of top 5 wins at HC Grand Slams.
On HC Andy Murray would not be able to separate himself from these guys at all. Chances will be that Nishikori and Delpo would not get injured constantly and Cilic and Stan would beat Murray many times on HC slams.