Clojure is quite maintainable, a well-written Clojure program is small and clear, easy to modify. Pervasive immutability is a huge win; Clojure programs are big on referential integrity.

There's some doublespeak going on here.

When "leadership" says "maintainable" what they mean is that the project is recoverable after they frog march the project lead out the door, or lay off the team, or the team quits because the job blows. Their view of maintainability is dominated by Bus Factor and similar existential concerns, rather than agility experienced by the project's authors. They actually want the opposite of maintainable: Rigid and heavily specified.