You’re conflating a number of issues. We are strictly talking about technical specifications. Not about who owns what nor even arguing that everything should be centralised. In fact it is technically possible to create a better alternative to SMTP while still satisfying all of the non-technical requirements you’ve outlined too. You could even drop feed that new protocol into existence the same way we’ve seen IPv6 creep in parallel to IPv4, albeit it would probably take 20 years to do so.
And this isn’t even touching on the problems with IMAP and the insanity that POP3 is even still a thing.
You are right - I may have went too far into blame assigning while explaining too little of my viewpoit. In my opinion e-mail protocols aren't but e-mail ecosystem is getting increasingly broken. Sure, SMTPv2 is _technically_ possible but I don't think it would be allowed to grow, mature and exist as a standard.
Last time I attempted setting up messaging accounts with beforementioned companies, it wasn't possible to use Mutt or bare Thunderbird - one had to use client software allowing some kind of RCE to set up access to those services. Add Google's bubbling[0] and Microsoft's repeated mail losing, and we no longer really have globally functional e-mail based on standards.
When some of the biggest actors don't follow rules describing delivery without proposing changes - yes - e-mail is being broken but not because protocols underneath are broken. It's because people trust these companies and possibly don't know that they may be victims of careful information filtering.
I have done some e-mail - related work for hosting companies in the past. For some years now, POP3 is not really a thing. It exists, it is being set up by mistake from time to time but the number of POP3 users compared to IMAP users was barely noticeable and I don't think it grew. I'm afraid to ask what your issues with IMAP are...
[0] I suspect that Google bubbles its e-mail customers just like its search users. Most non-technical people I know treat "spam" folder like it would literally burn their fingers upon touching. They act similarly, like trained to only look inside there when not seeing awaited messages in the inbox. Google delivering perfectly fine messages straight into "spam" folder has comparable results to Microsoft losing/destroying their customers' mail.
And this isn’t even touching on the problems with IMAP and the insanity that POP3 is even still a thing.