Would you consider .aero, .cat, .asia, .info novelties? They have been around for 20+ years. Sure, there are over 1500 gTLDs now, but when does something stop becoming a novelty? .ai a ccTLD, that Google recognizes as a gTLD, is that a novelty? These are a bit rhetorical.

I can't speak for the others, but registering a .aero domain requires submitting an application that's reviewed by a human and assessed based on the domain's relevancy to the aviation industry.

I would define them by the bar to entry. When a spammer can pick up thousands of domains for a few hundred bucks or less because a dodgy registrar is intentionally selling all domains on a specific TLD for next to nothing I find it safe to block anything on that TLD. I have always done this for email both personally and professionally and never once received any push-back. I explained the risk of collateral damage and leadership was always fine with it. Customers were B2B and could log in to open a ticket. Customer emails would come from domains we already trusted in their on-boarding process.