Plug_O_Stien

Yes, I concede that they do exist. But--and this is a MASSIVE but--it requires sacrifice. This is a low-magic universe, and almost all magic shown has required some degree of sacrifice, especially for the Valyrians pre-doom, who killed thousands a day. With the sheer amount of death occurring on that peninsula, I would be more shocked if they couldn't light a couple of candles, not to mention that most of their fire magic was tied to the 14 flames. Thoros of Myr coated cheap swords with wildfire and only managed to light his sword without it after bringing Beric Dondarrion back as a fire wight. Even after that, he now had to sacrifice his blood, as he had to cut his hand open to light his blood on fire. So when I read of some dude being able to light his hands on fire at no cost, it's very irritating, as it is one of the foundational concepts of this entire world. That being: there is always a price to pay, and magic is a double-edged sword. I hope that makes sense.

Yeah, I'm out. What a disappointment. completely broke the in-world immersion with this pyromancer nonsense.

Seconded

What is the one thing that both Sukuna and Kenjaku have in common/mastered? there is your answer. It really has nothing to do with mastery over domain expansion itself, its quite misleading. Open Domain is more like a mod then a direct upgrade.

The core idea of an open domain is quite simple. but it doesn't seem like the Mc knows it.

No-no, this needs to be made clear every time.

The gangster himself

You're thinking too one dimentionally. From the little information they have from the live stream, and his composure, its not impossible to assume that his upper limit might be close to Homelander. they don't have access to the system data's accurate stats.