Oh and, remember military basic protocols. Chain of command is still a thing Overwatch, Blackwatch and by extension Talon still use. Who's in command of the Talon side? Zarya and McCree are obviously in command of the Deltawatch side.

<Snipped quote by Sho Minazuki>

Blackwatch at this stage is disbanded.

As for Talon... you know, I originally wanted the Talon agents to be rather experienced (hence why you don't see them with advisors). They're simple but rather experienced agents. However, I can have like maybe Widowmaker come along to bring in extra support.

<Snipped quote by Lmpkio>

While being somewhat experienced is true, I think that calls even more reason to have everyone organized, that's what experienced soldiers do. Make a plan and protocols, stick to them, and having a chain of command lets them quickly organize themselves, even if their shotcaller and leader is killed in battle.

You can see it in the Sombra animation. The commander was clearly Reaper for the operation.

Having a chain of command doesn't expressly mean everyone has to listen to whoever is in command too. People can go and fulfill their own agendas like Sombra did behind everyone's backs.