1. You don't learn how to play chess against 5-year-old kids ... no ... you learn how to play chess against people who can actually play chess.
i.e. learning how to pilot decks in Casual is a waste of time ... you're still going to be bad at it when you hit Ranked and face off against an endless stream of fine-tuned decks people have scrounged from around the internet. You know you can actually learn from losing and making mistakes right?
2. Blowing off steam by playing a Tier 1 deck in Casual?!? Also ... what is fun/relaxing about going into a casual gameplay mode and facing off against the best decks in the current meta?
As for no hardcore palyers in Casual ... I used to get emoted silly when I played wacky decks in Casual ... with every "unusual" card I played I'd get a "wow" or something stupid like that ... people would send friend requests and call me all sorts of names/abuse in Russian (mainly) or broken English ... it got so bad I stopped accepting them (and sending friend requests) and even reported some players who said really offensive stuff in the past. I genuinley had a worse play-experience in Casual than I've had on ladder since.
Haven't played Casual in 3 years now (I think, maybe more) ... when Firebat started the Deck Doctor stuff for Omnistone. Casual is an asinine environment ... just look at the replies above ... I coudn't care less what the other player plays cuz I like midrange zooy or greedy midrange decks so usually have a chance against most decks. I usually include a favorite legendary card that is not commonly played (in the past they've included Dollmaster Dorian, Da Undertakah, and others - at the moment don't really have one, Naralex?)
100% agree with the original poster ... casual should be for fun meme-style stuff that you know will fail 99% of the time but just want to see if you can pull it off once without having to run into T1 face decks or combo decks all the time.
As far as making minor adjustments to top tier decks and play testing them in Casual ... just do it on ladder where you'll actually learn something useful ... what use is it knowing your deck with tiny tweeks can destroy a Roll the Bones Thief deck or meme deck? If you're not good enough to switch out two or three cards in a T1 deck and continue winning you are probably struggling on ladder anyway.
Then you have players like me ... who don't play Casual (anymore) and do everything silly in Ranked ... that quest to play x amount of Manathirst/Infuse cards? Build a deck with every single manathirst/infuse card for a randomly chosen class and hit up Ranked ... you'll be surprised how often you win ... and you can usually get the quest done in one or two games. (I should note, I don't play every day, maybe once or twice a week, so I don't have lots of time to just play one or two manathirst cards in a deck and eventually compelte the daily/weekly quest --- hence I have to concentrate the cards in one deck.) I'm currently running through all the Achievements for this and past expansions ... Pick a class and just throw cards into the deck that will get me the achievement ... B Positive - done ... Blood Bank - done ... A Graveyard Smash - done ... DIY Deathrattle - done ... No Swapsies Backsies - almost done. etc. etc. ... and the funny thing is I usually end up at the rank I started because I play cards noone is expecting which catches then off guard so I manage to win about half the time.
I just follow the advice Deck Doctor Firebat used to give out ... if you want to try out new stuff just do it on ladder, who cares if you lose rank, at least you're trying it out against the decks that matter at the moment ... if you lose 5 ranks then just metadeck and play what you are comforatble with to get those ranks back (or get the ranked rewards you want).