There is a huge difference between their initial expectations, and what actually happened. And now they are in too deep to undo their mistakes.
Regardless of what they said, they tried to attack the capital. That says more about whether they tried to take the capital than public statements.
You think those large amount of troops and resources, that were in the process of attempting to surround and take the capital were just sacrificed for no reason?
They spent a lot of resources on those attacks, and they didn't gain much from them.
Surely you should consider that it was a mistake, and don't think it was intentional for them to have taken such losses with little to show for it.
As in, they could have just not done a failed attack on the capital, and instead focused their troops on other regions to achieve some other goal.
However many resources they sacrificed on that attack could have been sacrificed elsewhere more effectively, which shows pretty clearly that this specific failed offensive wasn't some success and instead was a failed offensive that they had to back off on.
I suppose they can fortify that and come back in 10 years and take the rest.
Remember when Hannibal destroyed the Roman armies? That sure was humiliating.
What happened next?