I see MGS similar to American action movies. Its like finding relation between Japanese Samurai movies vs Spaghetti westerns. When I see style, many of the shots crib scenes from Blackhawk Down and Rambo and Western Films (with a Japanese twist). I don't know many animes have characters in the 60s stuck behind enemy lines, alone, and dealing with both political and mentor conflict.
You do know that there are also anime that deal with such broad themes as political and mentor conflict right?
It's more the casual use of extreme, high-octane bullshit that makes MGS closer to anime than action movies. What kind of western action movie has ambiguously gay vampires, skating-bombers, cyborg ninjas, magic (explained away by nanomachines) and people who got taken over by their fucking arm? I don't doubt that kojima is inspired by hollywood action movies but he's putting it through a pretty heavy anime filter.
Just look at shows like darker than black, jormagund, ghost in the shell and black lagoon. So much closer tone-wise to MGS than blackhawk down or rambo.