I think both dematerializer and banner need to be looked at

Right now these are co-depended. You can't nerf banner without making dematerializer significantly less desirable and you can't tune dematerializer down without making banner straight up as strong as when ZZ'rot was THE go to pushing item.

For banner the 100% magic resist needs to go away and switched to having an increased magic resist like how it has increased armor.

For dematerializer I think it is better to go with the route of making it offer increased damage to minions and monsters for those laners and junglers that prefer to get their farm on.

They would still have relations of being counter responses to each other, but to a less extreme state.