[dragonwriter]

> Then it should have been called "1.0".

6.c was described, both before and after its release, as being the “1.0” release of the Perl 6 language.

> More seriously, slow performance, missing features, bugs, etc. were part of the reason for not calling it "1.0"

No, they weren't.

The first “production-ready” release of Rakudo Star release was shortly after the 6.c spec release, in version 2016.01 (Rakudo Star uses date-based versions numbers.) If they were using semver-ish numbering for Star releases rather than dates, this would have been the 1.0 implementation (as opposed to spec) release.