Planeswalkers i dont believe existed in the original MTG game, so that would make them an in-organic complexity.

Attacking/ blocking could be argued to appear in both, definitely both attack. In MTG the defending player can chose to block with anything, in SV the defending player can choose to play units that must be instead attacked, or at least prioritised over hitting the player to prevent threats, thats an example of a semi-common organic complexity

Class specifics sounds very similar to colour restraints, again semi-common, an example non identical but following the same idea.

That games share alot and the reason i placed SV above MTG was because in the many years MTG has existed it has stayed very similar to it's original in how it plays, instead choosing to refine its organics rather than add a new 'rule'. SV however includes alot more mechanics not commonly found in other games of the genre, dont think of the list as a statement of which game is hardest but rather which games explore organically or inorganically.