So basically you want characters who have absolutely no stake in the Story nor the region of TW3 in tw3 because they appeared in tw2 where they had a stake in. The Queen has her valley of flowers to take care of (which is stated near the end of the game either by triss or yen) and dol blathanna is a long way from velen, and also from toussaint for that matter. Iorveth or Saskia simply don't matter anymore, the pontar valley is a lot of miles upstream of vergen not to mention occupied by nilfgaard. So your choice in either iorveth and a free vergen or roche and a vergen under kaedwen rule, don't matter in tw3 since it's all nilfgaard now. And a comparison with the ME Series is pointless, in ME you stay more or less in the same region of space, you always have the citadell as a meeting place, you don't have anything like that in the witcher games, maybe the palace of vizima but the place doesn't play a big role in the games anyway. In ME you shape the Fate of the Galaxy, in TW you can change the direction of a single little wheel in a very big machine. And now in tw3 you can do the same to a different wheel in the same big machine. Now saying that TW2 is ultimately irrelevant since none of the decisions matter in tw3 is stupid and shows you have not understood what the games are all about -> Geralt and not the fate of the world or even Galaxy.