That is false. There are plenty of inexpensive services that let you use an in-browser remote desktop client to test against many different web browsers, including Safari.
I just told you why those don't work. They don't have a real GPU so WebGL and other features don't work or don't behave like a real mac. Try it yourself against a website that uses modern HTML5 features. Same goes for audio.
But this doesn't use WebGL or audio, and in fact runs perfectly well in a VM, so what exactly is your point?
Also, "modern HTML5 features" covers plenty of things that work well without a GPU. It is only a tiny set of features that do not work. For the vast majority of modern sites, testing via a VM works just fine.
