At least the last time I checked, most Clash Royale and Clash of Clans players don't play with the best game pieces, because too much grinding or money is required for it to be worthwhile. In contrast, a much larger fraction of M:tG players (though still small in absolute terms) play with all the game pieces they want, and are only idea- and skill-limited.
Yes, in some sense the difference between M:tG's "~$50-500 for the best game pieces, or to enter major Limited tourneys where everyone is forced to start from scratch, for a year; only skill matters from there" and Clash Royale's "~$5000, or an amount of time and attention worth >$5000, for the best game pieces, otherwise you're strictly behind someone with higher-level versions of your pieces" is only one of degree. But again, a far larger fraction of M:tG games involve both players playing with what they consider the best pieces. I don't believe I'm the only one who sees this as amounting in practice to a difference in kind.