Stock market gains come from combination of inflation and increased corporate profits. Increased corporate profits come from either selling more on the top line (increased revenue) or better profit margins (becoming more efficient) or paying less taxes, or some combination of the 3. I'm not sure what something like the ratio of debt to GDP in China has to do with corporate profit margins in the US, but I could just be a simpleton.
If you don't like stocks, I'm open to analysis of superior investment avenues right now whether they be bonds or TIPS or whatever. I just can't find them. Stocks are on the high side of fair price right now, but appear cheap compared to other investments, especially with an economy that is doing just fine. Unemployment doing well, inflation appropriate, corporate profits rising at highest rate in years, etc. Will the good run go forever? Of course not, but the end certainly isn't likely to be near at hand. Stocks tend to crash after a massive run up or in a recession. We haven't had much run up in prices recently and recession nowhere near at this point.
Also, your numbers on debt are kinda misleading.
US household debt to GDP ratio is lowest it has been in a long time.
The basic argument against stocks is either 1) CAPE or 2) the world sucks and stocks have to fall. That's pretty much it. Neither is very nuanced. Neither cares that corporate profits are increasing at a rapid rate. Neither cares that the US economy actually isn't that bad right now, nor is the immediate future in much danger. Neither cares to examine alternative investments to stocks with as critical an eye.