One thing that's hard as a designer is recognizing your own bias, and accounting for it. I may play in ladder one night and see the same deck multiple times, and that deck might having amazing draws every time. It's super frustrating! But, that doesn't really mean the deck is too strong - humans just like to make patterns out of randomness.
We look at the large amounts of data to make those sorts of recommendations and work with Studio X (the part of the company that makes the cards) to figure out what is too oppressive to be in a format. Playing against the real meta definitely helps you figure out what you want to look for in the data.
Personally, I don't play meta-decks in ranked. I usually play this weird Bioessense Hydra deck I have, because I love it and it's fun until gold.