Let's not forget that Perl 6 was announced because Perl 5 usage was already stagnating. Perl 6 was supposed to fix that problem. But it ended up making it worse.
> The backwards incompatibility of Perl 6 absolutely killed Perl.
I think the backwards incompatibility was a minor issue compared to how long it took for Perl 6 to be released. It was eighteen years from the announcement to the first (just barely) usable release. And for a lot of that time, I was hearing tech leads say things like "we don't want to start this project in Perl 5 if Perl 6 is just around the corner."
At some point, they changed the narrative from "Perl 6 is the next version of Perl" to "Perl 6 is a sister language to Perl" - but they should have renamed it at that point instead of waiting another 5 years.
It's worth remembering that the Perl 6 project was started because Perl usage was stagnating. But the project was so badly managed that it killed off both Perl 5 and Perl 6 (now renamed Raku).
> The whole thing was written in perl 4 style OO Perl
What does that mean? Perl's basic OO support (using blessed hash references) was introduced with Perl 5 in 1994. I have no idea how anyone would even attempt writing OO code in Perl 4.