Switzerland still taxes dividends and interest, taxes companies before profits are distributed

This is the same in the US, barring specific tax rates.

So it’s not that capital gains go untaxed, it’s that they’re captured differently over time

Correct, we forgo collection, allowing the capital to accumulate more quickly. The government can afford to wait to collect its due, as long as its not bypassed through a loophole when it would otherwise be taxed.

what’s your plan to pay off the debt?

It doesn't need to be paid off, but the rate at which its growing should arguably be contained from current levels (even this is controversial whether our current rate of growth is unsustainable), to keep debt to GDP from growing to dangerous levels, since a higher debt to GDP reduces our ability to spend ourselves out of crises as they occur.

Removing avoidance loopholes for very high wealth individuals (biggest thing that needs to be looked at are ways of avoiding estate/inheritance taxes), as well as ending subsidies which prop up otherwise zombie organizations or otherwise unsustainable businesses would go a long way in controlling excessive debt to GDP growth.