Some time ago I performed some benchmarks of Formula Node and the conclusion was that the difference from native code is neglectable (until you don't use arrays in the node). But it was on single core machine. I think that difference you observe comes from execution parallelism.
Honestly, this is what makes the tool so appealing in the first place. If there's no overlays, using Windows Explorer is more advantageous to me. I hope they find some way to bring those back.