I think the main problem is everyone insists on over engineering a fucking website.
Moving apps into browsers is a step backwards for most apps and most users. I was using Jupyter the other day; it’s clunky as hell compared to MathCAD from 20 years ago. We use 1000x the computing power, literally, to deliver 10% of the experience. Keeps a lot of devs employed I guess...
You're pre-emptively trying to define what's useful for everybody else. That's the only way your premise works.
In my equally subjective view, XMLHttpRequest radically altered and improved the useful things you can do with the Web.
You can't use a 90s browser for Google Maps, Gmail, YouTube, nearly any online productivity software, and dozens of other common activities on the Web today. You would have to strip the services down to make them work, ie turn them into completely different products.
Simply put, most of the things most people do online today, can't function in a 90s browser. Just try using IE 5 or Netscape 4 with nearly any of the major Web services today. You can't. IE 5 with Facebook's non-mobile site? You have to build an entirely different product to make that work, basic interactivity drops to near zero.
1990s MapQuest sucked, big time. Google Maps is a radical improvement. How about simple things, such as smooth, fast, highly interactive stock charts, or real-time updating stock quotes, without having to reload the page constantly? 1998 browser? Nope.
Would the user experience be better if everything on the Web adhered to strict 1998 standards? That's an obviously subjective opinion. I don't think so. Do people like to see instant previews of the content they're about to post to Facebook or Twitter? When they click the little upvote arrow, do they like to see an appropriate reaction? When posting basic content or interacting with simple site features, do they like having to reload the entire page?
Let me guess... you’re a JS dev and you think “little upvote arrows” are where the real value is?
Clearly the users are wrong, I guess? Perhaps you should explain to them why your delicate design sensibilities dictate that they should download native clients because you think HTTP has gone off spec.
Let me guess... you're a COBOL dev and think computers should have never developer GUIs.
Not quite that old, but I was doing web and Java professionally in 1995, so I’ve seen it all.
The users are not wrong; they’ve simply been trapped in a local minima by inexperienced developers who would rather reinvent the wheel than make progress. Except every time the wheel gets squarer.
Other than that Email is a good example.
Let's take a step back here: the web is designed, from the ground up, for hypertext, interlinked documents comprising text and images, some of which are clickable and lead to other hyper-documents. HTTP - hypertext transfer protocol. "Web dev" should be referring 100% to things that happen on the server, which can be in any language you like, generating documents that are rendered as the end user would like. Forcing a thing designed for documents to run entire applications is what has gone wrong, it is, on the most fundamental level, an incredibly stupid thing to even try, but the entire industry did, and here we are today. It would be like MS declaring all Windows development henceforth will be in VBA macros for Word.
This is why the real engineering disciplines don't take software engineers seriously. You would never see a civil engineer try and construct a bridge out of some completely inappropriate material...