Fixing government and taxing the rich is the only solution that addresses the core of the issue. Charities can't close wealth gaps, because they lack the power to enforce laws that ensure fair labor and trade practices. Charities can't stop the healthcare industry from bankrupting sick or injured people, because that too requires enforcing the law. Charities can't stop concentration camps.
Charities do have a place in society and they can do enormous good, but can't compensate for a poor government.
Frankly, the notion that government is fundamentally ineffective and only the private sector can fix things is billionaire propaganda. Billionaires undermine government so they can exploit working-class people with fewer constraints. Then they'd use charity to launder their reputation while pushing their own agenda.
Deriding calls for fair taxes and claiming charities will fix things is wishful thinking at best.