On my Megumi can do open barrier domains original post, here a new post because I can't reply directly to that comment.
You're falling into the exact same traps that anyone else decrying Megumi's domain skills fall into:
no explanation on what Megumi was doing in the scene above in the open street
pulling an explanation of OBDs out and just deciding that Megumi doesn't fall into it
Megumi exclusively refers to a normal domain when he talks about his incomplete one
not being able to close a barrier with space altering properties doesn't mean that Megumi can't use barriers like the veil. He explicitly says that he can't place an artificial space of different sizes over reality. That's the skill he doesn't have
Megumi was ready to expand his domain in the street but he didn't because Reggie would've escaped -> meaning the skill to open a domain in the open in the same manner as Sukuna and Kenjaku is something that Megumi possess.
If Sukuna can do an open domain, and Kenjaku learned it after 1 thousand years, but Tengen can't even though she is the master of barrier techniques, then this tells us that OBD isn't just the next step of barrier techniques. This makes Megumi not able to close a normal domain barrier with space altering properties irrelevant.
But what could be a skill that helps make "painting on air" a reality?
Hanging your domain onto something that isn't your own barrier, maybe? A first step to discard your physical canvass and start painting on air. Like Megumi does against the finger bearer.
He uses a completely unique skill set no other sorcerer possess, to put his domain on top of someone else's barriers in a 1:1 ratio to reality. Then he expands his domain again, this time by using a physical structure aka a wall to hang his domain on top. After already confirming to us that he didn't need an external structure, while showing us that he now possesses a domain construct like Sukuna and Kenjaku.
Domain constructs aren't unique to OBDs, but taking the scene I've been talking about this whole time into context, it simply adds onto it.
The crux of the matter is:
Megumi doesn't know that open barrier domains are a thing, which is why he doesn't capitalise on what he can do and what he has. He thinks he has a second grade skill set even though Sukuna already praised him for what he can do: place his domain over someone else's
The other characters, when they talk about what Megumi did against the finger bearer, don't know that Megumi has progressed in his skills because right after the fight against Reggie, Megumi gets possessed. The others in Shinjuku talk about Megumi with outdated information
and even then they remark that what he did was extraordinary after the discussion started because what he did was explicitly compared to Sukuna's OBD
My very last thoughts on this:
An open barrier domain is not the mastery of barriers, otherwise Tengen would have one, but the mastery of domains itself plus the environment. For which hanging your domain on something that isn't your own barrier is the first step to master it.
And whatever anyone wants to reply to this with, if you can't talk about and explain what Megumi was about to do in the street, don't bother.
