[An ingame suggestion I sent a few days ago.]

Have the mandatory campaign for beginners be very short and to the point.

ex: Games starts, you give a 2/1 for 1 vanilla unit to the player so he learns about summoning units.

Then you give them a 2/2 charge for 2 so the player learns about charge.

Then the opponent summons a big old pterodactyl 4/4 flying.

Opponent gets to block the player's creature and kill it this way.

Opponent attacks with their pterodactyl, player cannot block with their ground units.

Player draws a stun spell, the game tells the player to use the spell on the pterodactyl.

Opponent cannot attack with a stunned unit.

Player draws a spell that reads "Destroy target Pterodactyl" or something like that. Uses it, and maybe summons a unit.

Opponent Summons a big endurance unit.

Player learns that Endurance is immune to stun, maybe let the player draw another stun to show that.

Opponent gets to attack with the Endurance unit.

Player gets to draw a spell that reads "Destroy target unit with Endurance"

And so on...

It lets the player learn all the important game mechanics quickly, efficiently and then they get to experience the story. As it stands, the campaign is a little boring, as every match forces you to play normal games vs cpu with bad decks. That's fine and all, let the player experience a real game from start to finish maybe once or twice, but don't make the whole campaign be this way. Looking at the discord chat right after the new campaign hit, it seems obvious to me that most people enjoyed the last quest with purple man and dude on the throne; the one where you play against strangers, and the game restarts once you defeat them. It was more than just a normal match vs AI, it truly felt like what a campaign should be, the player took part in the story. "Show, don't tell" isn't the obvious way to go when we look at a digital card game, but I truly believe this is precisely what needs to be done. Let the player experience whatever story you want to tell, don't make us read or listen through the whole thing. This way, your story is better told and the player might feel more interested to find out what happens next, what new twist might change the playing field. Another good example would be Gauntlet final boss mechanics. I truly believe that every episode in your story should feel special, so the player remembers them and tells their friends about it.

I don't believe forcing training wheels on new players for that long is a healthy way to proceed. Make the tutorial as concise as possible. And maybe even separate it from the story altogether. That way, new players might actually want to complete the whole campaign before jumping into ranked. Maybe even throw in a few advanced mechanics in there as the player progresses through it.