OS2 has a lot more easily accessible mobility skills which render bottleneck blocking even less viable, while in PoE you can very well do it all the time. Couple of deflection oriented chars in front make every dungeon in the game, plus a few other areas, a cakewalk. The open field requires a lot more control and micromanagement, I agree, but it isn't nonviable. OS2 leans more towards not having a tank at all, but rather an aggressive opportunist/shock trooper, which in PoE's terms most closely resembles a barbarian/melee rogue.
