Cash on Sidelines Myth

I've now come across a few variations of the following: https://www.pragcap.com/cash-sidelines-myth/

I take the (superfluous?) lesson on debit / credit accounting and agree that bid-ask is the ultimate driver of price. But I feel as though there are a couple of flaws:

1. We need to define what is meant by "cash on the sidelines"; to me, an increase in cash on the sidelines means I take my pay cheque and I deposit it in my brokerage account rather than use it to buy a car. The amount of cash I've earmarked to buy stocks can indeed fluctuate. COVID was an extreme example - a record number of people bottled up at home opening up an IB account and funding that instead of going out. The UOP here is key. 
2. If I'm wealthier and/or have more cash, then perhaps I'm more willing to bid up? 
3. How does Culler Roche reconcile his thinking with asset or sector rotation? No cash is created or destroyed, sure, and yet asset prices obviously fluctuate (fundamentally due to bid-ask but there needs to be cash to support the bid).

Am I missing something here.