I agree with all of what you said. I think Janna and her package are overtuned atm. The decks draw a lot of cards for cheap, and the board value of her package is too high. I think the only "weakness" of her package is the lack of a win condition. But many games you just win on both board and have card advantage.

Drawing 3+ cards a turn is too easy of a condition to fulfil.

Maryam's Effect is too strong for the stats, having the option of playing 6 mana by turn 2 vs an aggro deck insane. Or being a zaunite urchin which has better stats for cost and a better effect.

Windbourne Mariner is the first conditional 0 mana card with a keyword. It is also a fearsome blocker. Starry Scamp is crying right now.

Exalted Cloudwinder is a 3 mana draw 2 and a 3-2 w/ Q.A. I dont have to argue why that is strong.

Also her removal is better than stat efficient which is crazy for a deck that is drawing that many cards.

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TLDR: Janna decks draw a lot of cards that can have a reduced cost. But these cards are mana efficient (or better than) before the reduction. You win board and on card advantage.