I have to say that this "debate" is getting rather tedious to read or even bother caring about responding to when both people in the debate are talking past each other. Also that both of them are ignore the third, even simpler option, which is that no time travel or Shard travel is going to take place.

Instead of time travel and Shard Travel being red herrings for each other, both of them could be red herrings for the fact that all the travel we do will be taking place in the same shard in a linear fashion as the MSQ has always done. It's not like there's plenty of places to go on the Source that we've never been to before.