SVN branches were always cheap copies, right from the original version of SVN.
"svn cp http://.../trunkhttp://.../branches/foo" may not be the most concise command to type, but all it does is create a new item "foo" in a new revision, which references a previous item "trunk" in a previous revision. How many files/directories are under that doesn't affect how long the operation takes.
"svn cp http://.../trunk http://.../branches/foo" may not be the most concise command to type, but all it does is create a new item "foo" in a new revision, which references a previous item "trunk" in a previous revision. How many files/directories are under that doesn't affect how long the operation takes.