Because Kaibaman is essential for a Blue-Eyes deck and Blue Dragon Summoner is essential for a multitude of Normal Dragon/Warrior/Spellcaster decks like Dark Magician. Limiting/banning them would basically 🔥 the meta as a whole, in other words a majority of decks would be difficult to run
You can negate those effects and those monsters can be dealt with fairly easily. With what was said below, Blue Dragon Summoner is beneficial and almost necessary for warrior/spellcaster/dragon decks. Kaibaman, while frustrating at times, has definite balance in the game.
what a dumb question Kaibaman is The God for Blue Eyes! Thank God for him because u get a double summon pretty much and helps in events too especially dd tower
meta is not really matter, the matter is champion's vigilance make them too powerful.
strong monster by it self is not really that matter as long as spell,trap or effect is effective,even more reason when the card just need a not-so-hard requirement and no cost to pay.
also search power with only a few restriction is strong, but one which restricted a lot is fine,so bds is fine.
Utopia2003
CK15
