Fiendish chain is bad against XYZ decks and decks which can spam their field easily. It is better to flip your opponent's monster face down so he couldn't use it for another summon.
I don't know why someone would use fiendish chain against a monster that is obviously gonna be used as a material instead of using it on the extra deck monster in question
^ that's the reason why fiendish sees less and less play, combos now apart from summoning your boss monster give you advantage like adding or drawing cards, even if you stop the combo then you gotta deal with the boss monster, if you stop the boss monster your opponent already gained card advantage and they'll probably are ready to pull of the combo again next turn while stalling you.
When your opponent summons an extra monster sometimes it's too late. I was waiting with the trap ready, toggle on, my opponent summons some Stellar monster and destroys all my traps before I could even activate anything. Just one example
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