cat < file1 > file2 is not a UUOC. Classically, < and > do redirections which correspond to file descriptor duplications at the system level.
File descriptor duplications by themselves don’t do a thing (well, > redirections open with O_TRUNC, so to be accurate, output redirections do truncate the output file). Don’t let the < > symbols confuse you. Redirections don’t move data—they assign file descriptors to other file descriptors.
In this case you open file1 and assign that file descriptor to file descriptor 0 (<file1 == 0<file1) and file2 and assign that file descriptor to file descriptor 1 (>file2 == 1>file2).
Now that you’ve got two file descriptors, you need a process to shovel data between the two—and that’s what cat is for.
