I'd say it depends on what your character's economic status was before entering the dome. Are they a washed-up, pompous business-type that had to flee their city after mismanagement? Then of course they'd be shocked. But if they're poor and trying to make their living in a land of opportunity, then it might not be so unusual.
Hope that helps!
Withmore City has a possibly unique status, in that the entire place is literally owned by the corporations making up its Council.
I'm sure it's not the only place in the 2105 world where huge populations are similarly governed, tenanted, and shepherded by bare corporate power. Even in many places where the corporations haven't literally taken ownership of the very real estate the masses live on, you can bet that they essentially rule through their influence on the "independent" or even "elected" bodies that ostensibly govern. For damn sure you can bet that they exploit consumers and workers any way they can while externalizing waste, including the burned-out husks of "human capital" after they've wrung all value out of them.
No, Withmore isn't likely to be the worst slum in the world. In fact there are characters who have @histories along the lines of putting up with Withmore because they've been somewhere worse.