Blizzard should create a new format... for people who want to play fundecks... and they can do this by banning certain cards in the format, being wild, or standard... and every month the banlist gets extended with most played cards in this format... and unbanning cards from a class that is very little played... a dynamic banlist so to speak...
I'd never use that mode, though, because when I feel like playing a casual game of Hearthstone with whatever deck I feel like playing and no ranks to be gained or lost there's already a mode for that.
I'm aware that some players have created their own set of informal rules about what I should and shouldn't play in casual, and that those players might be upset when I break their rules. Some might even send me a friend request and try to explain their headcanon to me after the game, and others will just tell me to die of cancer, but I really couldn't care less about that.
To engage with your point a bit more seriously, though, I don't think that would work.
For example, I've mainly played variations of Curse of Agony warlock since that card came out I think during Barrens.
It's a bad deck, the sort that I think no one would disapprove of it I was to play it in Casual, but I just think that card is cool and I've had a lot of fun with it.
Key cards are Brann, School Teacher, Lady Darkvein, Tamsin Roame, Dreadlich Tamsin. Removing any one of those cards would tank its already poor win rate. Those are all super strong cards though, the sort that might get banned under your system.
Even bad, fun, memey strategies need good cards.
So even if I accepted in principle that it's wrong to play whatever deck you want in casual, I wouldn't even be able to play my crappy home-brew decks in your proposed format.
I switched from casual to ranked at exactly the time they brought in the rewards track and you started getting more XP for playing ranked.
If they made XP gain equal I'd switch back immediately.
The only thing the ranked system does is annoy me, I don't notice my rank until I start seeing those "you can't lose stars" messages. It forces me to be aware of my win rate, at least to some extent. Even though I don't care part of me feels like I've wasted time when I play for ages and ended up at a lower rank. And when I'm near a threshold I feel like I can't switch decks because I'll break my win streak.
Casual was always filled with people playing tier 1 decks, though.
I don't believe anyone has ever hovered over the deck they want to play, then thought "no wait that'll be no fun for my opponent" and switched to playing a different deck instead.
I certainly haven't.
Trying to police or moralize what decks other players play just makes you look silly. If you don't want to get beat by worse players playing better decks, play a better deck. Or concede and move on. Or petition Blizzard to create a "bad decks only" mode.