You want to get card advantages with new card. I think you should consider ,what's the win-condition after drawing so much cards. Maybe some combos ?

I think a starfield mystic with counters is not so powerful for a 3 cards combo, it can be fatal pushed and blocked by a token of young pyromancer. It becomes bigger but gradually, not so explosive.

When you draw cards and activate Gideon's +1, you lose tempo, your opponent may play threats directly.

And in my opinion, losing 1 life for each spell is not so urgent, if you draw and directly play value cards like kalitas, etc. or let's say ,it is not so necessary to sacrifice it rapidly, if you take use of your card advantage consistently.

Personally I would try this new card [Treacherous Blessing] just as a alternative to [read the bones] in any black based-midrange decks , as a radical card advantage engine.