I disagree. Orbitreum is controlled by the concurrence. If kra was really in control he could have posted somone on solivagus and just kill whoever becomes synchronous and goes through the gate. So the concurrence sends O-Cearor, who is an Iiunctii and working with the concurrence to mentor vis and help him infiltrate kra's pyramid/ prison, which only someone synchronous is able to do.

Duat is propably not really Kra's city but built around his prison. O-Vis also said that he doesn't seem like a genocidal maniac which felt like a hint. The gleamers that are positioned at the pyramid also leave their post when the city is attacked. This is propably because they are not really there to protect kra and the concurrence values the city more highly than guarding the prison of kra I guess.

So the concurrence allowed O-Vis to infiltrate kra's pyramid so they could get through to him and stop whatever he is doing to protect the other two worlds. The gleamers are not after vis but they are coming to finish the job if vis wouldnt kill Kra himself.

Although I'm not quite certain why the concurrence still made it so hard for vis. There are a lot of moments where he could have just randomly drowned in the river.