Ok, so which Diggle was the one who showed up in the finale? Cause he mentioned having a conversation with John that only the doppleganger would know about. But he can't be the doppleganger cause he explicitly mentions being from another Earth. Meaning he had to be the Other Earth Diggle from the start. Can't have it both ways.
Here's the thing, I don't mind it being on another Earth, but they should probably stfu about it until they can dedicate an ep dedicated to the nuts and bolts of it.