Not exactly. I talk about their relative growth, not their relative size. The debt doesn’t matter. There is no specific amount of debt, either nominal, or expressed as a percentage of gdp, that is definitely too much. This is because the USD is the global reserve currency and it’s issued by the federal reserve, which is part of the US federal government. Imagine you’re the bank in Monopoly, and you also own the monopoly money printing machine. There is no way you can’t pay for something in monopoly money, because you can just print more if you need more. That kind of devalues the existing money supply, but that’s a gradual effect, there’s no specific limit that this means.
I guess the bigger picture: money isn’t real. People need goods, services and infrastructure, not money. The country is prosperous if it can allow its citizens to consume goods, use services and depend on infrastructure. Whether the debt is 100 or 10 or 1000 percent of GDP, does not matter. What matters is if we can keep increasing the amount of goods we produce, housing we build, etc. Problem comes when those things slow down. The housing crisis, for example, in not primarily because of high interest rates (rates are not high and the crisis was already on when rates were historically low). It is because there are not enough houses being built in the places where it’s needed, due to shortages of labor and materials (and zoning, but that’s for another discussion)