If this system fails, the game becomes a frustrating, unplayable mess that bleeds players instantly.

While this conspiracy theory is widespread, the reality is much more mundane and focused entirely on mathematical fairness.
How You Are Ranked
Your trophy count is a numerical representation of your skill; win a match, and you take trophies from the loser.

This is why winning streaks inevitably end in a 'wall' of difficult matches; the system is functioning exactly as intended.
It only looks at your numerical rating.Accept the RNG.It helps them learn before facing real humans. The Free-to-Play Dilemma
The standard Elo system works perfectly for chess because all pieces are equal, but tower rush games feature upgradeable cards.

To combat this, developers have implemented secondary checks that look at the player's King Tower level.
System PriorityImportance LevelTrophy CountThe system will always prioritize finding an opponent within a 50-trophy rangeKing Level / Card LevelsThe system tries to match levels, but will abandon this check if the queue takes longer than 10 seconds True Fairness
This is why all true esports tournaments and competitive challenges utilize the 'Tournament Standard' ruleset.

When levels are equalized, the matchmaking system shines, ensuring that the better player almost always wins.