cp and mv should more behave like their UNIX pendants, in terms of how they deal with existing directories as targets. I.e., files should be copied/moved inside a specified existing target directory.
E.g.,

cat src/dir/file
value = a

cp src/dir dest/existing-dir
cat dest/existing-dir/dir/file
value = a

Additionally, to easily copy files from one dir to another, the * operator should be introduced, i.e.,:

cat src/dir/file
value = a

cp src/dir/* dest/existing-dir
cat dest/existing-dir/file
value = a