You missunderstood in D2 -> Damian was defeated and banished (which he is during BD and D:OS2), came back AND defeated Lucian the second time with a compromised dragon. Sometime after that D2 starts. So yes it is the latest.
True the black ring fortresses do have certain design elements similar to the void, but the "corruption" that we saw during OS2 never appeared to be there.
Apart from this official timeline it can be argued that both Original Sin-parts exist in a different timeline. Since especially in the second one some serious changes were done in personality of characters, and a lot of things that seem important are simply not mentioned in the other games lore and vice versa. But so far we do not have a certain explanaition why they act so strange and clash with their morale and lore.
Sadly Larian has the (IMHO) bad habit of jumping back and forth in the timeline with each game so it is never 100% certain what happened why and when exactly.
Last edited by MAsterX; 18/03/18 04:14 PM.