You're dealing with different sets, different card quantities, and varying purchasing fees
This will help the supplier process your claim more efficiently and ensure you receive a full replacement promptly
That being said, I don't have that same luxury with the more obscure decks so generally speaking, unless there's a lore specific reason of limiting cards to certain quantities due to their uniqueness (for example only 1 copy of each Crystal Beast existing), 2 or 3 copies are acceptable in order to preserve the feeling of the deck as it appeared in the anime
The anime juices this ability a little bit by saying how Dragon Master Knight gains extra attack power for every dragon on the field, including an opponent's, as well as any dragons in the graveyard
The designers had created a story that they wanted to tell, and they designed the cards in the set around that storyline, often resulting in a unplayable or weak cards
Throw the new D-Force (YGOrg Translation) Spell into the mix, and they cant target your cards either, plus Plasma itself cant be destroyed by card effects, gains ATK, and can attack twice