Of course, if you train an LLM heavily on narrow benchmark domains then its prediction performance will improve on those domains, but why would you expect that to improve performance in unrelated areas?
If you trained yourself extensively on advanced math, would you expect that to improve your programming ability? If not, they why would you expect it to improve programming ability of a far less sophisticated "intelligence" (prediction engine) such as a language model?! If you trained yourself on LeetCode programming, would you expect that to help hardening corporate production systems?!