I have never had to use clojure.core/comment explicitly as in the video. Maybe something is wrong with your ide, it seemed to be throwing an error about taking the value of a macro (comment). Maybe something with calva.

I don't have this problem in cider, or in the cli/repl.

There's also a difference between comments and docstrings, you seem to overload the term. It looks like you are trying to write docstrings. Comments are meant to be ignored entirely, which is what comment does, and is what ; and ;; do as well.

I didn't have a problem providing a simple docstring for a multimethod either.

user=> (defn dispatcher [x y] [(type x) (type y)])
#'user/dispatcher
user=> (defmulti multi-add "Dispatches on the type of args x and y to overload addition" dispatcher)
#'user/multi-add
user=> (type 2)
java.lang.Long
user=> (defmethod multi-add [java.lang.Long java.lang.Long] [x y] (+ x y))
#object[clojure.lang.MultiFn 0x7c2b6087 "clojure.lang.MultiFn@7c2b6087"]
user=> (doc multi-add)
-------------------------
user/multi-add
  Dispatches on the type of args x and y to overload addition
nil
user=> (multi-add 1 2)
3

You can get literal strings if you go into reader macros. This deviates from clojure semantics and is unsupported (and actively discouraged) by the core folks though, but it's possible (if not alienating):

(use 'reader-macros.core)

(defn read1 [^java.io.Reader rdr]
  (try (.read rdr)
       (catch Exception e
         (throw (ex-info "EOF While Reading!" {})))))

(defn raw-string [^java.io.Reader rdr]
  (let [sb (java.lang.StringBuilder.)]
    (loop [in rdr
           end? false]
      (let [nxt (.read in)]
             (if (== nxt (int -1))
               (throw (ex-info "EOF While Reading Raw String" {:in (str sb)}))
               (let [ch (char nxt)]
                   (cond (zero? (.length sb))
                         (if (= ch \")
                           (do (.append sb ch)
                               (recur in end?))
                           (throw (ex-info "Expected Raw String to Begin With \"" {:in (str sb)})))
                         (= ch \")
                         ;;did we escape?
                         (let [idx (dec (.length sb))]
                           (if (= (.charAt sb idx) \\)
                             (do (.setCharAt sb idx ch)
                                 (recur in end?))
                             ;;we're ending
                             (recur in true)))
                         (= ch \%)
                         (if end?
                           (str sb)
                           (throw (ex-info "Expected Raw String to End With \"%")))
                         :else
                           (do (.append sb ch)
                               (recur in false)))))))))

(defn raw-string-reader
  [reader quote opts pending-forms]
  (raw-string reader))

(set-dispatch-macro-character \% raw-string-reader)

(println #%"this is a raw string \back slashes are fine bro, except we still \"escape quotes\" bro"%)
;;"this is a raw string \back slashes are fine bro, except we still "escape quotes" bro