It is easy to have a high win rate if you selectively pick the time period. I have something insane like a 78% win rate with Jhin (my main) over the past 25 games. However my overall win rate for this season is closer to 53%, it is positive but not insanely so. And as one might expect from this I have been slowly increasing in rank as I play.
Runs of wins and losses happen all the time, they happen in league where your skill gets carried from game to game (and thus having some small measure of consistency) and they happen in coin flips where there is no hold over at all from one to the next.
The main difference is that when the run is a bunch of losses people feel bad, sometimes REALLY bad. They start to look for solutions, reasons why, some connecting factor that explains why they could be winning THEN losing. But until you start looking at all your games objectively, look at your wins just as harshly as your loses, you are going to keep coming to biased conclusions. Ones that result more from the feelings you bring to them than any actual fact.
I've seen similar complaints in a lot of games, that they are being kept down by the system and should be winning more. But I have yet to see anything to actually make me believe that is truly the case.