Aktchually… SS benefits are pretty progressive. Those with lower lifetime earnings will see a much higher income replacement percentage than higher earners up to that $165k-ish limit.
Lifting the taxable income cap would not fully eliminate the funding gap. We’d also have to pay out more to those higher earners too. If we didn’t, it would change SS from insurance to wellfare. And that would lead to (Republican) lobbiests fighting even harder to privatize, limit, or end SS.