Not so sure about the heart of magic yet, since we haven't seen any positive or negative impact from looking at it.
Dominic giving himself up is a writer flaw and not a character flaw.
If it was only Dominic sneaking out and surrendering to save his friends, it would have been a mistake made by a character.
But when all the protagonists agreed to this action, never bothered to contact the right people before he did, and didn't even consider an alternative plan, that's not Dominic's flaw.
The way Dominic treats Celesto is the same thing.
It's not just Dominic since the rest of the gang treats him the same way.
And all this is without mentioning the news posts, that usually consider the character's actions to be "cool".
The only exception so far is the ominous post about the cost Dominic will pay for looking at the heart of magic. If it actually develops into something, I'll count it as Dominic's character flaw.
Edit:
Sneaky
Future