The causality is reversed for public debt though - governments react to deflationary environments by increasing public spending to compensate for the private sector's propensity to save - as a "spender of last resort" as it were.
That's how Japan ended up the way it did.
Arguably it should have spent even more to offset deflation in the 90s.
Again, we're at levels record levels of global public debt. There is no free lunch. Debt financed spending is only possible through financial repression (real default through inflation in this case and in the 1940's following WWII, the last time US debt reached 130% of GDP) which ultimately drives speculation as capital searches for yield. Rinse repeat deflationary shock as a result.
We are seeing this now thanks to wealth inequality brought on by capital being given preferential tax status to labor for decades and stagnant wage growth again for decades.
This wasnt a problem following WW2 - wage growth was high and given vastly preferential tax treatment to labor.
The stock market is where savers have been forced to. Pensions included. ZIRP/negative real rates have consequences. There "isn't too much capital". It's being misallocated due to misguided policy. It will get worse.
You need to start thinking in second and third order effects.