This breaks down with the fact that it's really difficult, outside of really constrained spaces, to turn a "what" specification into a high-performance implementation, so any practical language needs to let you give some degree of control in the "how", and as a result, any modern language is somewhere uncomfortably between the 3GL and 4GL in the paradigm, not fitting entirely well in either category.
I think we’ve had at least 4 generations of that idea that reducing coding time will be a game-changer: the COBOL/SQL era of English-like languages promising that business people could write or at least read the code directly, 4GLs in the 80s and 90s offering an updated take on that idea, the massive push for outsourcing in the 90s and 2000s cutting the hourly cost down, and now LLMs in the form being pushed by Gartner/McKinsey/etc. In each case there have been some real wins but far less than proponents hoped because the hard problem was deciding what it really needed to do, not hammering out syntax.
There’s also a kind of Jevons paradox at work because even now we still have way more demand than capacity, so any productivity wins are cancelled out. At some point that should plateau but I’m not betting on it being soon.
It wasn't true, although they did make some operations easier in tangible ways.
Rust is a wholly different kind of thing -- not easier than, say, Java, but lots more control with better guarantees. It's more a systems programming language. 4GLs were all application-focused.