(If a permanent with a stun counter would become untapped, remove one from it instead.) The value of X is calculated only once, as Omega's ability resolves
Take a look at MaRos articles describing new sets - he does not just dump the image gallery and say let me know what you think - he describes the sets design goals, the mechanics, why they were chosen, how those mechanics were placed in each colour, the limited archetypes the set was designed around, some anecdotes about the design process, etc
For example, if they have a haste creature you'd rather Electrify, then you don't have that opportunity
Shoot, if you add in a self-sacrifice option, you could Mind Twist the table and then set up a later nasty draw
By 2020, 19% of all new card designs were legendary
Its making me contemplate being active for a season and playing in person constructed, just to get all of the goodies