2 threads can run on 1 core (without HT) sequentially and this problem can still exist. More commonly if you don't have the right locking.

Yes, and from this we can conclude that single-core processors are distributed systems too! It's counter-intuitive from an architectural (i.e. teleological) perspective, but it makes perfect sense when you approach it from a suitable level of analysis (intentionality).

It doesn't because memory is shared, clock is shared. Some of the tougher challenges in DS don't reside in this situation.

>It doesn't because memory is shared, clock is shared.

You're arguing your point using the definition that I argue is insufficient. We're running around in circles.

>Some of the tougher challenges in DS don't reside in this situation.

Yes, and others still do. We can definitely agree on the fact that it's an easier variant of DS.