What is the strong argument exactly? Odin coexists happily with Zig, Rust, C3, nim already, no?

Odin is different enough from those languages, where coexistence and what is offered should not be so much of a problem. Unless, out of sheer competitive or corporate spitefulness against others (the less, the better thinking) and for higher rankings, they feel compelled to reduce user choice.

Jai, on the other hand, arguably appeals to the same groups and circles as those that are or might be attracted to Odin. That even appears to go for their creators, where similar demographics of fans would likely choose Jonathan Blow.

I think plenty of people will still use Odin, primarily because there's a lot more batteries included, but everything about this announcement makes me think Bill is worried about the competition, and trying to showcase his 1.0 with all his batteries...while releasing around the same time as jai. Kinda weird behavior imo.