I personally got into web development with jQuery. Some years I go it was a must, now a days, I find it unnecessary and I don't use it any more. Is this just me or is transition people is doing ??
a) smoothed over differences between browsers. With the web being taken more seriously by everyone, the browser implementers are much more careful about all following the same standard so with every year that goes by there are fewer cross browser quirks to worry about (it's still a major pain today though)
b) providing convenience methods for manipulating the dom and working with data etc. I think jQuery has less of a role to play since ES5 and ES6 are how javascript is written nowadays and have more advanced features than js did in jquery's heyday. Also, for advanced client side apps, frameworks like angular and ember also provide such features.
I think once web apps starting getting larger and larger, jQuery became more and more of a hinderance (since it offered no framework for structuring apps).
Had the world gone with one of the many other options back in the day, I think we might be in a better place already.
It would help if you told us what insight we missed about MooTools that would have made the world a better place? Why jQuery has made it such a miserable one?
MooTools and other libraries might possibly be more powerful if you are developing in Javascript in general, but for web development I primarily care about DOM manipulation, and it was much easier to pick up jQuery than anything else at the time. It's a mistake to think that languages should win out simply based on functionality and capabilities, without taking into account things like ease of use and learning curve.
ES7 wanted to introduce an Array#contains method. But due to prototype extension issues like https://esdiscuss.org/topic/having-a-non-enumerable-array-pr... , they had to rename it to Array#includes ...