lets find out... *one Op.gg look later
Well just at looking at your last 4 days of ranked matches you had a KDA of 7.3 / 8.3 / 9.8 with I believe 47% kill participation
Meaning you're dying more on average then you are contributing to the win. Now not really anyway for me to know why, but even in matches where you win you still are racking up to 11 deaths in a match.
I haven't been playing ranked a lot but have tried lately and just got to Silver. I'd be happy to watch a match of yours to give you feedback. (I aint no guru but I'm rockin an 75% win rate and am averaging half as many deaths as you are haha)
More info goes into your MMR rating then just wins vs loses