They really aren't when you are operating at ISP scale. Especially when there are 20+ years of evidence of said scoring systems being abused until they calcified into the mess that is modern email hosting

Really don't understand what "unacceptable" even means in this context. It is perfectly acceptable for a company to control internet access.

More to the point though, what is this cheap and easy domain scoring system that does a better job than a blanket ban?

The best domain reputation provider, DomainTools, definitely isn't providing their data for cheap, nor is it always the fastest. We pay a substantial amount to them for thousands of requests a day, something we reserve for enriching actual security incidents, not because someone wants to go to catparty.foobar or whatever.

Unacceptable for who? It's definitely more than acceptable for a lot of people.

You say this as if the people implementing TLD blocks even understand what the term scoring system means

Sure, but blanket bans are even cheaper.

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.