Why matchmaker is not balancing my W/L ratio at 50%?

For the last 20 games my W/L ratio is 5-14. It's "a bit" lower than 50%. When I was playing before the long break I was at Silver I (didn't play ranked for like forever), then didn't play at all for a year or something. I've returned and it's defeat after defeat. It's ridiculous. Even when I'm playing ok, the team throws hard. It looks expected draft level of my teammates dropped while of my enemies stayed the same, as if I didn't quit for more than a year.
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