React definitely didn't make frontend _great_ in a lot of cases, but jQuery, mootools, prototype, knockout, ember, angular, and a whole lot more JS frameworks that have come and gone predate React. If React hadn't been invented there'd be just as many poorly developed browser apps as there are today. You can't really pin that on React.

Part of me hopes that without React (poorly) filling the void, something like Elm could have gained traction. But ultimately I think it’s unlikely.

I think you might be forgetting how much it sucked before React.