A lot of these spells also provide smaller buffs , so feel free to use them as part of a kill plan and not just to keep John alive
So much value that Snapcaster Mage is routinely seen in Magic's most competitive and expensive formats
Im sure you want to try a version of that in Commander, dont you
(Scryfall note) When the triggered ability resolves, first the player whose turn it is (if that player is an opponent) chooses which creature they will sacrifice, then each other opponent in turn order does the same, then all chosen creatures are sacrificed at the same time
In some unusual cases, the card you reveal from the top of your library may not have the same mana value as the spell your opponent cast, but you can still cast that card because the resulting spell does have the same mana value
After all, therell always be players trying to make EDH turtle decks work