I have 15k learned. It's a question of timing. Can time spent making the card outweigh time saved learning it? I would say yes. It's easy to spend too long making a single card. A compromise is to make a small card at first and improve it whenever you fail it.

Personally I need some context in a card to hook it up to other things. Such as the sentence where I first encountered it. Without that I will often fail the card over and over and waste time - it would have been quicker to put some effort upfront making a decent card.