It would be amazing if there were other languages available for front-end development in the browser, no? Even if you think that JS is so wonderful, then having competition would still be good, or no? Currently JavaScript has a monopoly in the browser and monopolies are always bad. Bad for innovation and everything else.

It would be better if there were no oddities in a language. One of the reasons why everyone hates PHP is that it is full of inconsistencies, odd design choices, weird naming and unexpected behaviour. JS has at least some of these.

If there was a second of third language available in the browser, then that too could be used to develop back-end applications and would have the benefits you describe - that you can use the same language for both stacks etc. For example - if you could front-end stuff in Python, would it be amazing or bad? Or would the current JS devs just fear for their jobs because of it?