Having done the gauntlet of S70 to S97 a few times before getting to S+ I wouldn't agree that it's a matter of luck. Granted there are a few games where your team's weapon combinations just don't mesh, I think in every loss in the 90s I could identify what mistake I was making. Every loss was on my failures and I'd learn from that. In the final win streak from S69 to S+ I had 2 or 3 losses. How I played then was significantly different than the week prior, and I think being able to recognize my own faults and how to improve; learning to use the map, take out enemies, and completing the objective are what contributed to this.
So don't sell yourself short if you made it to S+, it'd take too much luck to get there without some help from you.
That's advice for anyone in any bracket, to recognize your fault every time you're splatted, every loss, and how you could have made that into a victory.