We all agree than 80% of games are decided on who flipped a coin better.

There is a simple solution to that. Just make all viable decks slower; if the available mana is very low because everything is decided on very few rounds then the difficulty is low so everyone plays their decks well; only if the game slows down the skill cap increases because only then there is more available mana and more card plays in the same round which increases the likelihood of higher skill cap and eventually a feeling that what you did mattered and when you failed: that what you did can improve.

PS Take for example the highest skill cap deck in the game right now (quest mage); the average match time is at least 9 minutes when a typical simplistic fast deck("aggro") can go as low as 5; if you lose with the mage deck it's usually either because an aggro deck didn't even give it a chance to do anything or because you fumbled your chance when you had a billion choices and you didn't make a good enough choice.

PPS One could argue that this would make the game more boring by ranking slower; there's an easy solution to that; if it makes for example the ranking 30% slower then just make the stars being accumulated 30% faster so it equalizes on that front.