Sure, but I don't call "+" addition, it's just Perl's "plus operator" which happens to be defined over numbers and strings.
Personally, I don't see why every language is trying to copy Haskell's monads. A monad is not some deeply important concept, it's just an abstraction that happened to be very useful in the context of Haskell's type system. Without Haskell's type system, it is not quite as useful, and it's possible that other abstractions would be better.
Sure! I'd be happy to agree with this statement.
Functors and pointed functors and arrows are also quite important.
 Though not the most important one.