> today's new devs have been spoiled by modern UIs (and that's a good thing) and shouldn't have to cope with Emacs and its stubborn retroness.

Two words: Programmable editor.

One of the best advantages of Lisp is the ability to metaprogram. After solving a problem, you find that your code can fit other cases and then you you write a program that will produce the relevant code for those cases. In most other PL you would have to write the slightly different code again or use a template language.

Once you get accustomed to that, you will start to decompose other parts of your workflow in smaller building blocks and realize that only a few parts differ, but they all fits the same workflow. And one of the main realization 99% of them are text, act on text, and produce text. So what you really need is a framework around text, not a bespoke assemblage of tools.

With Unix, you have the text processing tools and vi (some would say ed). All centered around the terminal, the shell and files. Emacs is another version with a lisp vm, a collection of functions and the buffer as the interface. A third version is acme with buffers and mouse clicks as commands. The idea here is to be able to build small tools that can take care of the misc. things we need to do while writing programs. From navigation to analyzing, from formatting to building, and the myriads things in between.

Modern UIs are good for beginner and light usage. Or if you're lucky, they have your specific workflow neatly packaged in some plugins. But when you get tired of having another helpful "update" messing your muscle memory, or want to establish an efficient workflow with some external program (A CL lisp runtime in your case), that's when the weakness appears.