If this were strictly true Perl would not exist.
Hogwash. The problem presented is one of an experienced programmer in language X starting a new project in language Y. This is entirely different from the problem of a language designer, expert in both languages X and Y, creating a new language Z.
However, the importation of powerful idioms such as map, grep, foreach, et al, in no way restricts the expressiveness of Java. Quite the contrary, they have the chance to cut through the verbosity and rigidity of standard Java, thereby making the language more usable.
It's a possiblity, but I think the risk outweighs the potential gain. This might work out well for an experienced Java hacker that already has all the standard Java idioms at his fingertips. Mixing in some Perl might be a big help. However, for a Perl geek trying to swim in the Java swamp, these imported idioms will essentially act as a crutch. Worse, they will render his code unmaintainable by normal Java programmers. All in all, I think this is best avoided.