You are exactly right. My favourite is when resistance to APL-family languages comes from people who claim to be polyglots, and you ask them which languages and they list: C, C#, java, javascript, VB, ruby, python etc. Those are all really the same language with slightly different wording and details. Like german and english. APL-family is like Mandarin or Japanese. Lisp is like Latin (in fact lisp is really a mechanism to author your own language with s-exprs). Obviously, these languages won't be comprehensible to you until you put the effort into learning the abstractions... this isn't like transitioning from C++ to Java where you can broadly carry the same concepts over.
There is nothing difficult about reading these languages to people who use them, anymore than it is difficult for a musician to read sheet music. In fact, APL languages have less ambiguous parsing and precedence rules which I find make them easier to read.
> Those are all really the same language with slightly different wording and details. Like german and english.
I'd argue you only think that because they've opted for a familiar syntax. E.g. the object model (or lack of one) is vastly different between these languages and they employ drastically different type systems.
Ruby is closer to Smalltalk than C in most respects other than syntax, for example, and provides most of the abilities lisp gives you, including the ability to define domain-specific languages. The major aspect you're not getting from Ruby would be homoiconicity.
Here's and article comparing Lisp and Ruby[1].
I'm not saying learning languages outside of this group isn't important, but that a lot of the reason why languages like Lisp and APL are seen as so different has more to do with syntax than semantics. Most people don't know what the semantic differences even are, because getting past the alien syntax is too much effort. When you do, the differences aren't all that huge.
There is nothing difficult about reading these languages to people who use them, anymore than it is difficult for a musician to read sheet music. In fact, APL languages have less ambiguous parsing and precedence rules which I find make them easier to read.