Not at all
Theri barrier is open - meaning they haven't closed it, allowing for an escape
Without a barrier in place, the domain wouldn't have its sure hit effect. Which both Sukuna and Kenny have, clearly
Otherwise Megumi would have the same feat as them.
Again, you're confusing barrier with the Area of effect of a domain.
The function of a barrier in a domain is to constraint enemies to one place.
A domain is the user realizing their technique into a temporary place. Ie, them painting in a canvas. The canvas is the barrier in this case.
But, barrier less, ie, painting on air, is different.
In that it doesn't require a canvas/barrier.
They can realize/paint their techniques and surefire hits directly on to the area around them.
The area of a barrieless domain's effect =/= a barrier.
Kusakabe's explanation works well here.
Imagine a regular domain.
A water bowl
The bowl is the barrier/temporary space.
The water is their innate technique.
And the surefire hits are whatever they can do with the water.
Now, a barrier less domain.
They don't need a bowl to hold the water.
They can hold the water to a circular shape without a bowl, and also manipulate the size of that circle. It's like telekinesis. It's still in a similar shape to a normal domain. But the outer shell, ie the barrier, ie the bowl, is not necessary.
And since it still has a shape, they can still use surefire hits.
What Megumi did was, he couldn't create a bowl to contain his water. So he used the buildings as a bowl and poured his water into it. The water is held in shape by the buildings. Not telekinetically like Sukuna and Kenny does.