The entire JavaScript ecosystem is a mess, because you have languages built on-top of other languages, with subsets of those languages it's a mess.
As we know JavaScript is a language, but it is also a subset of the ECMAScript language specification. ECMAScript also has other compliant languages, such as ActionScript and JScript. ECMAScript also has a couple of different versions, at the time of writing, 1, 2, 3, 3.1, 5, 6 (2015), 7 (2016), 8 (2017), 9 (2018) and next (Beta).
And so it's valid to say you have ES2 compatible ActionScript. Assuming it exists. Just like you can say you have ES9 JavaScript.
But it doesn't stop there, JSX and TypeScript build on-top of JavaScript and ES6. But they also add more to the language. But JSX can work with TypeScript, and so following your suggestion we should tag all JSX TypeScript questions with, ecmascript-6javascripttypescriptjsx, leaving one tag for any information that isn't about the language. And with so many libraries in JavaScript you need those tags!
You also have languages like CoffeeScript that transpile to JavaScript, but don't extend it or ECMAScript. And "isn't it the case that many of the same concepts of the latter apply to the former?" So this should include the JavaScript language tag too? Should we include ECMAScript too?
As we can only have 5 tags, we have to be a little bit sparing in how we use them. I suggest following the Python tags. All Python questions are tagged with python, if it works in one version then you include python-3.x or python-2.x. Things like IronPython and Jython are different versions of Python and so would be the sole language tag. But can also include the version tag. jythonpython-2.x is ok.
But if the question includes all the language tags, and any other tags that would make sense then I see no harm in having the following tags javascriptecmascript-6typescriptjsxangular. If the person is doing a programming challenge then it's more than ok to change the tags to javascripttypescriptjsxangularprogramming-challenge. But if you just remove the tags for the sake of it, then I don't see it as an improvement. As the tags aren't wrong, and it just reduces the discoverability of the question.