Isn’t exactly this kind of thing what is mostly responsible for the demise of Perl?

As I heard it told, the developers of Perl worked so long & hard on the next version after Perl 5, but then veered off to make a new language (Raku) and despite the reality being otherwise, people feared so much that Perl would die (i.e. that 6 would never materialize) that in the meantime “everyone” had switched to Python (despite it clearly being an inferior language - hehehehe:-P).

So that would be a “con” I suppose, if fights over which language is better ends up diluting efforts to work on or with either.