I love clojure with CIDER but I have heard as a REPL experience it doesn't compare to CL with SLIME. I like emacs as a lisp machine but I know that a big ball of mutable state and functions with side effects on a single thread really doesn't live up to a proper lisp machine.

true. I don't have the energy to learn emacs fu. An actual lisp machine would be dreamy.

Clojure REPL experience is pretty primitive though, you don’t have a step debugger or something like the conditions system, being a hosted language you only get stacktraces from the VM.

Supposedly this is the bees knees and better than a stepper:

https://www.flow-storm.org/

(haven't use it myself yet)

But things like CIDER give you step debugging if you want. For whatever reason it always felt clunkier than ELisp's debugger

I came here to say this as well. The various Lisp dialects I've used still offer this rich REPL experience today. Other languages haven't caught up.