Should you be demoted if you can't carry games in your current rank?

I found the enemies to be numerous as oppose to skillful when I would battle them in team fights in the past five games yet I lost every single game and I would be toxic if I blamed my team. My team was terrible each game and the other team just dominated them. I played the best on my team and sometimes the best in the whole match in the last five games so I take the blame for not carrying but should I have to carry to not get demoted? After soaring to S1 only to hit more toxic/bad players sinking me to S4 I finally made it to S2 only to hit this last string of bad games. I got demoted to S3 after 5 games where I got A-S scores and fielded questions in the lobby such as "This is a new account, can I play mid?" Which was asked in the 5th and deciding game before demotion. If I knew the solution for this I would develop video games, who do we know that develops video games and should consider putting more time into match-making? Or maybe everyone thinks it's fine to have a fill team filled with toxics on games that demote or promote you?

I dunno.