Nah, if I set up even Sonic will be able to get me 8/10 times, unless its a tight corner for the sniper like the field entrances on donner. Ive set up in every place possible on Donner, Kalt, and Anzio. There are places where the nades wont be able to go without the rifleman exposing themself first and any good MG will get a prey that stands out in the open like an idiot. Every time you have MGs in the sniper house windows on Kalt, its going to be a Sniper or a good rifle who gets them out (Of course the occasional support will get inside the house and bash their head in)
Now if an MG is being a non-eGO allowed name and camping in the far, far back of the map close to his first flag when your team has the rest of his flags then yeah, (s)he can be a bit of a pain to get for a sniper, but not because the MG is set up in a great spot, its because th spawn waves come out and the sniper had to deal with the Supports and Assaults running down the street at him
For the part of your quote that I bolded: Set me up in the best spot on any map with an MG, and stick Sumac, Blue, or Ron on that map with a sniper and see who wins. Spoiler Alert: It wont be me