Actually I misspoke, it's new accounts that aren't supposed to get matched up with accounts with extensive collections. I admit I can't find the blue post and it may have just been something they said at Blizzcon, but it's not too hard to see the system in action. Make a new account and you won't see crazy legendary filled decks until much later than usual.
Last season I barely played on my main account, so it sat at rank 15 until near the end of the season. When I started pushing for legend on that account again the decks and player skill levels encountered were much higher than what I was facing at the same ranks on my secondary f2p account. So while I can't provide you with a blue post, it's really not a difficult thing to test once the season is halfway over or so.