The '90% of outcomes are decided by dice' aspect makes [Hearthstone] a very poor game, which IMO is the bigger problem, and got MUCH worse with the last expansion. Does anyone, winner or loser, feel good about a game being decided by the dice behind Unstable Portal? And you can't build a deck with limited luck factors, as some of the best cards (such as unstable portal) are also the big dice roll cards.It's true that Hearthstone has a lot of cards with random effects. However, I don't agree that this specific element makes Hearthstone more or less skillful than Magic.
First, randomness is just probability. Probability can be factored into your plans. You can mitigate the randomness with tactics. Yes, sometimes you'll get very unlucky. But over time, skillful play that accounts for probability will win.
You can see this because the same people tend to win, tend to put up consistent records. That is a sure sign of a game that requires skill.
It's like poker. Poker is very random. But it's still a skill-based game. Randomness in and of itself does not exclude skill.
Second, there is a huge source of randomness present in Magic that is missing from Hearthstone: resources. Magic requires land cards in your deck. Drawing the right amount of land is a huge factor in determining victory in Magic. In fact, a good deal of skill goes into constructing the mana base for a given deck. Almost every new player makes decks with 20 land, which is a mistake (unless running extreme aggro). They need to learn that the more correct number is 24 lands. A lot of the time, the endgame in Magic can come down to who draws a threat versus who draws an unneeded land.
That source of randomness is completely missing from Hearthstone. There is no mana-screw or mana-flood in Hearthstone. Resource gain is not random, but completely predictable.
From my perspective, Hearthstone and Magic have similar amounts of randomness. Hearthstone merely moves the randomness from resource generation to gameplay effects. You can still play skillfully with random effects. You just have to take probability into account, and have backup plans for being unlucky.