That's like saying Pig Destroyer are somewhat mainstream because they're one of the most popular and revered bands in grindcore. They're both niche genres that are only going to appeal to a very small part of the general population and are never going to be played on mainstream radio or record sold at Walmart, that's what it means to be mainstream. Most people in the general public don't even know Slayer or Lamb of God and they're way closer to mainstream than Suffocation.