In other words, it wouldn't be superior according to the way I understand it. Learning curve, existing libraries and solutions all matter in this comparison..

For me it'd have to interact seamlessly with other languages and enable incremental adoption, otherwise you can't swap one with another.

But you can swap a floppy disk with USB flash drive if the PC has an USB port, so that's what I mean by superior..

Your original premise is flawed; there can never be language that is superior in every aspect. Almost everything is a trade off. A technology that is good for one purpose might be wrong for another and vice-versa. Also a new language will always start with no adoption, no experts, and no libraries so that is also a trade off.

A language that allows incremental adoption will necessarily be limited by that necessity -- another trade off.

When USB was new very few computers had USB ports but nearly all computers had floppy drives. Floppy disks were cheap and flash drives were expensive. If your purpose was to share data then using a USB Flash drive at that time was an inferior experience. If you had a lot of data, a writable CD was a much better choice. If there was ever a period that USB drives were supreme for that task, it was brief. With higher speeds and greater adoption, it quickly became much better to use the Internet to exchange data.

>it wouldn't be superior according to the way I understand it.

Money is the biggest parameter, and it would not make number go up in the short term. Tech stacks are in inherently a long term investment and companies are conservative to do big reworks like that.