That seems to me jumping ahead quite a bit. My understanding is interest paid is a measure of investment income. If all corporations pay 5% then couldn't we just calculate their value as a factor of that?

Naturally, we would want more money for a corporation to hold it longer, than shorter, because they would need to pay for the duration risk. When that inverts, it's basically saying that the long term risk is no longer important because anyone who would invest would only do short term. There's not enough confidence for long term investing, or it's not confident at all.

Long term rates are not based on new issuance, they're based on old long-term issuance repriced. That seems to get lost in the sauce ;) Am I missing anything?

I'd make the argument the Fed can't do much about the situation. If you're not confident in the future you're not confident in the future. Sure, the Fed could lower the price of money, but you still need confidence in the future and they can't control that.