Thus Spake Zaranephilpal/WhatInfernalsCantDo

Now, as to what Infernals can't do:
1) Be perfect in an endeavor, rather than a specific approach to that endeavor.
2) Develop without invariably limiting and defining their bodies, minds and souls. You can't cherry pick your way out of this.
3) Develop extreme competence in one theme without losing some competence in opposing themes.
4) Suck.

I may be biased on #4, but you can probably trust the first three.

...

I would be strongly against letting Heretical Charms smooth off the flaws of other Charms. In some cases, you can shift a flaw to something equally constraining, such as how Adorjan initially attacks loud noises and then develops an avoidance response as you approach the Silent Wind herself. However, being an Infernal is about accepting limitations in the name of power. Heretics don't ever get to avoid that-- they just get to explore new limitations, too.

Source: [1]