The longer Vettel continues to struggle next to Ricciardo, the worse it looks for him. It's not looking great already. It's odd, because I still struggle to convince myself Ricciardo is anything special, which would make Vettel average, and he isn't. It can't be that clear cut.
It probably is a tendency towards adapting to the blown diffuser-less regs. He was the master of getting the most out of the exhausts, so to go from stamping on the throttle at an incredibly early stage to feathering the throttle with all this torque must make it harder for him to adapt than others.
I'm not convinced his heart is quite where it was last year either. He was flying home at the earliest opportunity during testing, understandably with a newborn, but perhaps it demonstrates his sole priority isn't F1 now?
Regardless, I expected a 4-times champion to have adapted a bit quicker than this.