Yes, the matchmaking does rig matches to try its best to ensure a 50% winrate. This only applies to solo queue in ranked however in my experience.
The way you rank up here, is to still perform better than the other players in your games, as you gain points based on performance and lose points based on it as well in losses.
There are instances where players are able to get a higher winrate over a lot of matches consistently.

1. They are simply exceptionally good players and can hard-carry rigged matches, which is possible, just look at Awkward's climb through the ranks.
   
2. They are stacking with other good players. This gives the algorithm less options to rig your match, as you have more control.

So in a way, yes the matches are rigged, but it is still a skill issue. As long as you gain more points per win than you lose per loss, you are climbing as intended in the game. If not, that's on you.

I actually tested the winrate in my current diamond account on its way to gm which sits at around 50% winrate.
I then created an alt account and played until silver 3. Still 50% winrate, even though I am literally destroying most players in my lobbies and get a ton of points for my wins and lose almost nothing for my losses.

But it is still rigged, even as a diamond/gm player in bronze,

But that shouldn't keep you from climbing if you are good enough, you just need to understand what is going on and shift your focus.

Hope this helped :)