Both posts you linked to are over a year old, so you can ignore both of those (although the first one isn’t talking about moving elements in the element tree)…
Reordering elements in the Element tree has never been possible until literally a day ago (see this announcement from yesterday New Responsive [beta] Drag and Drop in Elements Tree - Announcements - Bubble Forum).
So now (as of yesterday) it is possible, and very simple - just drag an element in the tree to another position, or into and out of parent containers.
Note: this feature is only available in the new responsive engine, not the legacy engine, so if you’re still using that you won’t have this feature.