This is intended. The territory editing in gangs is only for their personal territories, which is most circumstances won't change from a Settlement. I'm keeping the territory editor there for anyone who wants to adjust anything they want to their own campaign rules.
The Dominion territory system is managed by the Arbitrator, the Campaign Admin. This puts the onus and maintains control of dominion territory assignments on that admin (or any other admins enabled) to edit the controlling gang of dominion territories. So territories on the gang editor are split between Gang and Campaign territories.
It was important to many players that only an arbitrator could both control assignment of territories to gangs and therefore also be able to govern the flow of battles over territories somewhat. If a player group simply wants everyone to have full control, they could make everyone an admin.
Does this make sense?