Every HN thread on economics has a bunch of comments like these that are earnestly misinformed about economics. When commenting on something outside of your wheelhouse, please recall Socrates from the Apology: "I observed that even the good artisans fell into the same error as the poets; because they were good workmen they thought that they also knew all sorts of high matters, and this defect in them overshadowed their wisdom."
I'll point out just two deficiencies in these threads and leave the rest to you. If P/E ratios in the US are "too high," then people would invest their money elsewhere for better return, right? Maybe international stocks or bonds or whatever. And why don't they, if they have every incentive to seek a better return? Because there are no better returns, even in countries with higher interest rates. So how could P/E ratios be too high? The more likely explanation is that this is the "new normal" - savings outpaces investment opportunities for many reasons (aging populations, growth in countries with stronger saving cultures, etc.), which pushes up the premium on assets.
Second, on the subject of interest rates and QE, a little international perspective would make you reconsider the effect on the overall economy. All other developed economies have lower interest rates, more QE, and slower growth than the US. Look at Europe, look at Japan. The issues of "why are asset prices rising" and "why is inflation low" are much larger than just US policy. We are talking global trade and demographic factors that influence these things. The current stance of fiscal and monetary policy is the symptom, not the cause. And in fact the US has been significantly more successful than our counterparts on that topic, as a fast and strong response in 2008 pre-empted the kind of drawn out economic malaise seen in Europe, where the ECB waited years before easing policy to the degree that we had. Now Europe has lower rates, more QE, lower inflation, a worse labor market, and less growth than the US. And that's before factoring in the coronavirus crisis. Policy may have increased inequality in some ways, but if you're going to make that claim you have to also answer the corresponding counter-factual: potentially the poor would have been even worse off (relative to the rich) if there were no policy interventions and the labor market collapsed. There have been some papers on the topic, and it is not at all obvious that inequality is worse now than it would have been if there was less policy intervention.