Well "infinite power", broke the inverse tiering system, and as
you mentioned yourself, people with similar potential has reached such levels of power, and exceeded it.
The only time Isabeau reacted to her was when Tart was mid-air no? Every other time was Isabeau trying to attack Tart but getting blitzed every time.
Speaking of Isabeau though (Since I'm currently checking it to respond) Kyubey mentions that when she was born (So right off the bat this was at her weakest) she encompassed all of France, and then her daughter proceeds to mention: "As the Dark Age reached maturity, all of the people felt the darkness of their losses! It
created (meaning it has already happened) an even larger witch, spreading farther and wider over
the world!"
Isabeau's invulnerability also includes abilities, such as
Melissa's Matter Destruction hax.
So we probably need to add
Statistics Amplification (Grows more powerful and larger accordingly to the despair of men within her Barrier) alongside a more detailed
Invulnerability and upgrade her accordingly.
As for Doppel tart, I believe it was because it of the entire "
No matter who or what stands before this Doppel, it shall find sin within them and expose it before the light of day. In short, one has no choice but to accept the full brunt of its absurd purity."
Though "ceaselessly disgorge their sins", doesn't this mean the Doppel forces them to talk about their sins with her aura?