Recently I watched a video by Brian Kibler about the differences in culture between Magic: The Gathering and Hearthstone. He correctly notes that Hearthstone has a culture focused around the idea that the game is all luck and skill doesn't matter, while MTG has a culture that supports the idea of skill being paramount.
These aren't all or nothing ideas! Obviously there are plenty of MTG players who whine about getting mana screwed and Hearthstone players who correctly acknowledge that the game has a pretty large skill ceiling. That said, the trend of Hearthstone players talking about RNG and MTG players talking about skill is real.
Kibler thinks that this is in part because of explicit randomness in a lot of good Hearthstone cards - cards that summon a random minion or make a random spell, for example. MTG has less of that. Also the average MTG player plays in tournaments, whether they be small scale Friday Night Magic kind of tournaments or Pro Tour Qualifiers. Hearthstone players play on ladder and only a tiny percentage take part in tournaments of any sort.
He also thinks that MTG content creators tend to write serious strategy articles while Hearthstone creators make silly decks to play on twitch and youtube and this changes how they are perceived. While Firebat may bring really tight decks to tournaments he still makes stupid Blood Bloom / Doom decks to play on his stream because those bring more viewers in, so people see top Hearthstone players doing stupid crap all the time and don't see the skill that goes into perfecting and practising a deck.
Kibler's points are right on, but there is more to it, I think.
I remember when I was playing MTG a lot back in Thunder Bay when I was a teenager and it was easy to see that skill was a defining factor. I won about 25% of the tournaments I entered, and one of my close friends won another 25%. Mostly anyone else who won was also somebody I knew because generally we were all in the top 8 in nearly every tournament. When much of your life in a hobby involves tournaments and you see the same people winning every time you really get the impression that skill is the dominant factor.
When I played against good players in top 8 situations I played tight and quiet but it was entirely different in the early rounds against newbies. If I rolled over someone whose deck really needed some tuning I would often sit after the match and go over their deck to give them pointers. We would talk about cards they needed, land ratios, what decks other people were playing, etc. Usually those people would leave some new ideas and also with the definitive impression that I beat them because I was better, not because I got lucky.
In Hearthstone you never get that experience. When you get beat you just lose and queue up again. Nobody who crushes you on their way up the ladder sits down with you to say "Hey, you know, your deck could probably use a couple more 1 drops and cut a few expensive dragons." You don't get people saying "You would have beaten me if you had just Fireballed me in the face on your second last turn." Lacking those cues it is easy for the player to just rail about getting unlucky and move on.
Hearthstone players also consistently play people of a similar skill level. The ladder pairs you against people who have won about as much as you, and tournaments are full of top tier players. You just don't have the newest scrub going into a big tournament, meeting a pro, and getting beat because the pro plays better, at least not nearly as often as it happens in MTG.
When you play against people who are equally skilled, *of course* the victory comes down to RNG. There is room for individual skillful plays, but on average against a similarly skilled player you would expect somebody's luck to break better and take the victory on that basis.
So while there is an advantage to pitting all the noobs against one another, it does make them think that the game is just RNG based, and the pros end up in the same boat. Hearthstone pros don't have as much experience at grinding through noobs as the MTG people do, so their games often come down to a single instance of good or bad luck because skill is already controlled for.
This isn't something that needs fixing. It is just an emergent, accidental property of the way the games are played, marketed, sold, and viewed. Both companies are doing it right, considering those considerations, but those choices really do affect the way players think about the games they play.