But is that enough to combat her EX tonfas, her armor breaking, her high damage combos and her mobility? Sure hellsparks adds to the space control of Shinnoks but after that, he's left for the fishes. His low damage output is horrid in comparison to Tanya's, his mobility outside of backdash is decent, and half of his moves are slightly negative. Outside of his wakeup (which can easily be baited), he has nothing to defend himself against.
Perhaps, my match-up experiences only cloud my judgement on this match-up but this isn't an advantageous match-up in his favor.
Tanya's damage isn't extraordinary in the slightest, her damage is good not great. Shinnok can't rely on combos for high damage, that's why he has the 10% fullscreen attacks in Necro and his vortex in Boneshaper and Impostor. Back to Necro, I'm still not convinced the Tanya matchup is as bad as you say.
"After that he's left for the fishes". I assume that's referreing to Necro's fullscreen game vs Tanya, as in outside of Hell Sparks range? Teleport could indeed allow Tanya to punish Necro's fullscreen attacks on whiff, but I doubt that can be done on reaction. Tanya's own fullscreen game is ass in Dragon Naginata and not great in Kobu either.
His backdash is insanely good and MB hell sparks is an incredibly move. There's also no such thing as an easily baitable wakeup. Can't 90% of the cast's wakeups be easily baited unless they're a 50/50? The person waking up has to also think about using a wakeup.
I kinda want to see this matchup in action to be honest, this is all just theory talk. I don't play Tanya however, though I do have sort of a Necro.