Current AI is entirely incapable of generating the balanced and fun/engaging rule sets required for a MtG style game. Sure the art assets could be generated with skilled prompting and touchup but even that is nowhere close to the strong statement you made.
OP likely meant that a Midjourney-level AI can easily generate all the card art.
Obviously, current AIs cannot generate game rulesets because the game feel is an internal phenomenon that cannot be represented in the material domain and therefore AIs cannot train on it.
