It is until it's not. That's the problem. The AI gets tripped up at some point, starts frigging tests instead of actually fixing bugs, starts looping then after several hours says it's not possible. If you're lucky.
Then on average your velocity is little better than if you just did it all by hand.
The AI gets tripped phenomenon is something I've experienced, and I think it's again related to context usage. Using more agents and skills will reduce the pollution on the main context, and delay the moment where things go weird. /clear after each small mission.
As said above, CC needs heavy guidance, but even with these issues, I'm way faster.
Then on average your velocity is little better than if you just did it all by hand.