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

Many players believe that matchmaking is intentionally rigged against them, constantly forcing them to fight 'hard counters' after a win streak.
Trophy and Rating Systems
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.
There is no 'anti-deck' conspiracy.If you face a hard counter, it is pure statistical variance.In the lower arenas, the system often includes 'bots'. The Problem of Card Levels
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 PriorityWeightTrophy 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 The Esports Standard
This is why all true esports tournaments and competitive challenges utilize the 'Tournament Standard' ruleset.

The algorithm is blind; it only respects victory.