Some do. Yes. I'm creeping Plat soloq as we speak. That said a high rank 3-5 stack that plays together often has a higher chance to win than a team of solos. Until there is a dedicated solo q there will be a wall hit by the vast majority of players.
It's the same in league and r6. The cream of the crop players have the capacity to go above and beyond in solo against stacks. Anybody below them will hit a wall against stacks. Its why there was a huge push for a soloq option for siege. Once you get into high gold or Plat it's a good idea to start looking for a dedicated group of people to play with consistently.
I guess I could have worded my initial response a bit clearer lol