That's not to say that my experience somehow means more than yours or is more valid. But I personally think my experience is more representative of the average layperson. You're welcome to disagree.
I specifically said the technical world. Most people I know are technical to some degree and almost all of them would assume cryptography when they hear the word "crypto".
I work with people who all have hardware crypto, you are right that we do not have the organizational knowledge to verify everything with crypto. Even if the tech is 60% there.
What other kind of verification are we talking about which standard email DKIM doesn't have.
A message signature means I got you to do something like tap a Yubikey and enter a PIN, touch a fingerprint sensor, etc. That can still be socially engineered, of course, but it can’t happen by accident and you could add some safeguards against routine by having a dedicated “major transactions” key used only for that purpose to add a physical speed bump.
The problem is that “ignore my gmail, I list my phone” will defeat that training more often than we’d like, so you really need to have process safeguards which make it a requirement and management backing to say even the CEO will follow the lost device process rather than asking someone to bypass process, and that has to be so carefully enshrined that nobody questions whether their job is on the line if they tell the real CFO that they can’t bypass the process.
Laptops and mobiles have all the same sensors. Most big companies have organization wide password, fingerprint and auto screen turn off requirement. Obviously not all companies follows good security practices or doesn't give secure devices(with sensors and encryption), but if that is the case Yubikey isn't going to save them.
Your telco's NOC can at best track what "port of entry" the call came from but can't force the Caller ID go be truthful.
These things are usually discovered but not before a call or sms goes through. There are also other possibilities such as diverting calls available to someone with the right access to the signalling network. Anything that's unauthenticated and unencrypted should be regarded as insecure, really.
I've heard of stir shaken but I recall FCC ordered it mandatory multiples years ago. Did that not happen?
The authencation above is between the terminal and the location registry (simplified, there are several other components involved). Not internationally between the telcos.
There is literally no encryption that could handle this. By that logic if I bribe or hack yubikey company, then they could ship malicious batch of yubikeys. Or I can bribe or hack microsoft/apple to get root access of someone.
"Can you buy $1000 worth of egift cards and text me back with the redemption codes? Our jobs depend on this. I'm in a very important meeting, otherwise of so it myself, left my private key at office and can't sign this message right now."
The human element remains the weakest link.