I'm pretty confident that Gmail is more secure than the domain registrar if you're really attacked. At least do your research carefully on this one. Domains do get stolen.
As always, consider your own threat model. But if you're a civilian? Wow, just hope you can walk away from the lockout.
At that point, registrar can't do much to harm you.
Choosing your country's TLD for the most important domain is probably a good idea, if your country has well functioing and fair TLD manager. I certainly feel I have more of a chance when someone steals my country's domain, rather than some .com or .org. Country domain can be registered only to citizens, and so both the TLD manager and the thief will at least be in the same jurisdiction as me.
The entire process also seems rather lengthy to me if all you want is set up secure email: https://www.icann.org/resources/pages/accreditation-2012-02-...
Having said that said, I haven't had a failed delivery in years and I host my email on a cheap VPS. I only started getting deliverability problems when I ignored my mail client's (and server's) warnings before sending a 100MiB email through a mail server that also hosted a TOR relay, which was pretty stupid in hindsight.
Mail deliverability isn't quite as bad as people seem to think it is, but if mail delivery to the big four fails, there's almost never a way to troubleshoot it. That's kind of a pain, I suppose.
Of course, it just shifts your risk to the domain registrar, so don't use someone too cheap. It's worth paying a decent fee for decent service here.
If you want real identity security, reg your own domain, and move it with you.