Wire transfer is not really the point. It became a topic because that was posed as an "instant" way to get money out of a brokerage. I pointed out it isn't always reliable and that unreliability is a symptom of a real liquidity difference.
The point is that if I demanded money from you, you can give me your money out of a bank immediately, simply by walking into one. You cannot get money out of a brokerage account for me. You need it transferred for you to a bank first before it becomes your money. This is an actual difference to me who wants money from you now and it's not in theory.
I guess for me it’s extremely rare for me to need (large amounts of) money “now” apart from daily needs but that’s usually charged to my credit card and paid off from my Fidelity cash management account on an interval.
I can see in emergency situations where that is true. But the currently level of liquidity that I get with brokerage accounts + cash management account works for 99.99% of my use cases.
I’m willing to take the higher interest in MMF for what is a negligible impact to liquidity for my use cases.
The point is that if I demanded money from you, you can give me your money out of a bank immediately, simply by walking into one. You cannot get money out of a brokerage account for me. You need it transferred for you to a bank first before it becomes your money. This is an actual difference to me who wants money from you now and it's not in theory.