The action is being applied on all files as it is running stepwise. That is, unless you're calling the action from another and running it grouped. For ten files, you're executing 6 statements. If you were running grouped, you'd be running 60 statements.

The gating factor is the Add to Apple App statement which displays each file it is working on in the status bar because the iTunes/Music method of adding tracks is terribly slow. As a test you can disable the Add statement and you'll see everything happens almost all at once. (depending on the Save being local, external, network, etc.).

The Yate interpreter emulates parallelism by having a statement performed on all selected files before going on to the next. However, once in the real code it is not launching threads to perform the operation. For instance on a Save, each file must still be individually saved.

Most of this is fine except when interacting with Apple Apps for some functions. Even launching multiple threads would not help as iTunes/Music processes them, one at a time.