While I generally agree with your comments, I am currently working on a project with a React front-end in Typescript and a Node back-end in Typescript, the first time I've ever had the same primary language everywhere. It is a HUGE productivity boost, and most importantly makes it much easier for anyone on the team to review and understand pretty much any area of the codebase.

Folks should not underestimate the benefits of having a single primary common language everywhere.