150 trillion is low. If you include government debt, unfunded liabilities, various financial obligations (private debt and shadow banking) and DERIVATIVES it gets MUCH higher. Like in the quadrillion range according to some. It's an important distinction because it speaks directly to the debt market. There isn't enough dollars running around to cover all of the existing obligations. If/when it goes south there WILL be defaults. It doesn't even have to be in the quadrillion range to do that. Just the lowish trillions. It's important because the blowback onto the GDP should a significant black swan show up will be huge, which will in turn affect all manner of money flows to the governments of the world, not just the US.Good discussion on Debt and Interest Rates from WolfStreet. Most of the debt (esp that $150T) just isn't going to be paid or at least not with any form of currency that has any purchasing power.
TLDR - current average cost of funds for the US is @ 3.4%. We have 6T of re-fi slated this year alone. (Using a 10yr Note as an example) on the roll, that debt is to be refi'd @ 200+ basis points more, driving the weighted average cost of funds. Some say we can go to 5% before it hits the fan. Regardless - this is the story of gradually, and then all at once.
Couple of other factoids:
For every $1.00 of stimulus (public money spent into the economy to generate more public wealth) the return is currently @ $0.15.
@ 19% of all income in America is transfer payments
@ 70% of the US Econ is Consumer Spending (*consider these last 2 together)
Current Debt to GDP is @ 130%. That rocket ship took off in 1981, and on a graph (regardless of games played under Clinton in the 1990s) it is has been a virtual straight line on the graph, @ 20 yrs we'll be at 200%.......unless of course the World tires of Modern Monetary Theory and WRC / Treasuries which can be confiscated via sanctions prior to that - kinda bet it does.
We saw some of this unwinding in the aftermath of the GFC with the dark pools - it couldn't be fully determined who owned homes that were being repo'd. A few took it to the courts and won. If that were to happen at scale it will be catastrophic.
Your analysis of the declining return on stimulus is spot on. The only way out of this is either a financial reset or government default.