You seem to never, ever play Scarlet Blaze don't you ?
Death Mirage cancels 1 debuff from main himself and 1 debuff from a random ally, which means it can be total wasteful in a lot of cases. And the extra 20 chakra will only grants an extra mystery, which won't kill anything unless the power different is HUGE.
Now compare to other classes.
Root of Warrior can grants immunity to up to 3 ninja, which include Sasuke. Killing Intention of Warrior + Root of Warrior + Sasuke's barrier is the real death formular.
Water main standard heal can remove every debuff on the ally with lowest HP, which tend to be the one with most debuff. EVERY DEBUFF. EVERY ROUND.
Earth main, while maybe vulnerable to debuff, can create sturdy shield that is hard to take down. Steel Boby, you can't get a combo on him, making him really hard to kill. Those 2 aspects make Earth main very annoying, can stonewall players stronger than him into a default.
Giant Rasengan with Gaara's barrier is monstrous too, while Dance of Impetus can help you cast one single-target mystery twice a round, and THAT can kill 1 ninja on round 2.

Long story short, you can spin any main into an OP character if you want. But if you want to do that, at least play the * main before talking. If you have play Scarlet Blaze, you will describe his skill on how it works, not on how the text said, which is half gibbrish and seriously misleading.

For Christ's sake! You fight a team with Gaara and Naruto then proceed to blame Fire main for being too OP ?
And what the heck is "end's up reflecting para on Sasuke" even mean ? Only dumbass would cast non-prompt skill right when the round start, and if you are not that dumbass (still not understand where the "reflecting para" come from) you would be blissed to see a debuff reflecting on Sasuke.
On side note, a Fire main with Death Mirage is sitting duck for interruption. Other character can cast their mystery right away leaving a small time frame for the opponent to react. A Fire main need to trigger Death Mirage first before casting mystery, which leave a huge time gap for the opponent to react so don't whine about that passive is OP.