Without getting into the other points raised, let's look at this spell.
Elemental Engulf: TN 5t, rg 5, Dg 1/2/3
+ Blast TN 7t, rg 5, Dg 1/2/3b
+ Blast TN 9t, rg 5, Dg 1/2b/3b
+ Blast TN 11t rg 5, Dg 1/2b/3bb
+ Increased Damage TN 13t, rg 5, Dg 2/3b/4bb
+ Increased Damage TN 15t, rg 5, Dg 3/4b/5bb
+ Alter Range TN 17t, rg 10, Dg 3/4b/5bb
+ Ice TN 20t, rg 10, Dg 3/4b/5bb, slows
+ Ice TN 23t, rg 10, Dg 3/4b/5bb, paralyzes
Even if a character starts with 3 Tenacity and 5 Sorcery, they are incapable of ever casting this spell. The spells requires 4 Immuto, meaning they must have 2 Grimoires (including one designed and assembled by the Fatemaster) and the Mastered Immuto Talent (a minimum of 3 Pursuit steps), but their stats still won't be high enough to cast this. If they try to lower the TN with more Immuto, they need to take Mastered Immuto again (a minimum of 6 total Pursuit steps). If they fulfill two steps of their fate and use both Aspect increases to boost their Tenacity, two cards can cast this spell. If they increase their aspects and also specialize in Sorcery to add a tome to their totals, 5 cards can cast this spell. So the spell requires 3-6 pursuit steps, two confrontations with fate, and direct assistance from the FM to function, and even then the spell is cast by ~9% of the cards in the deck. Still doable, especially since you can lower the TN by removing unnecessary Immuto, but not really something that happens "all the time".
Unless you circumvent that with Hedge Magic. The real problem with this spell seems to be that you can add two Ice Immuto for free, essentially knocking down the TN by six and removing the need for a talent and second grimoire. The three restraints on magic built into the system— TN, need for advancement, and Fatemaster intervention— are all bypassed with Hedge Magic's Magical Talent. A free Immuto is about on par with the bonus from other Magical Theories (which all come out roughly equal to a Talent), but the ability to ignore TN increases is not functionally mitigated by the need to only use spells with that Immuto since this kind of mage is focused on damage instead of utility anyway. Maybe if the talent allowed you to ignore the first TN increase from applying the Immuto it'd be less insane, but as is it's clearly out of line with other abilities. Despite generally being a very permissive GM, until this ability is given an errata, I'd have no problem either banning it or else striking the text about ignoring increases in TN.