What is the system of forming teams behind the normal match game?

Playing LOL in 2018 is the worst gaming experience! Especially the Normal matching system. U know what? I have been a LOL player for 4 years get highest rank of Platinum 2. During 2017 I did not play much because i was busy with school. I just picked up LOL recently at late 2017 and 2018. Since I haven not play LOL like a year my level of skill is not what as before, but your system is keep matching me with those players that way higher than my level of skill and my team got crashed every time. What frustrating more is that I tried harder and played seriously but the opponent was not what I can outplay no matter skills and level of strategy. For me every game seems hopeless to win. Even the opponent's team pick support Chap to top or no ADC team comp, we could not win and got outplayed because we are not the same level of players, that is more frustrating . I deleted the game today and I will picked up HeartStone where is more friendly to returned players that I know I will not get Crashed every time no matter how hard I tried because their ranking and matching system is way better than yours. Today I had the worst gaming experience I could every had. Even when I lost 10 games consequently in rank, I still have the confidence to keep matching for next game. After these days, no LOL is not as friendly to me as before! GB.