The KISS principle should apply to task force design. The more missions and general running around you tack on, the less people are going run it - they simply won't have the time or stamina. Zone-hopping, kill-alls, and street hunts are especially egregious in the "tacking on extra time for no benefit" department and should be kept to a minimum if not eliminated.
As people have pointed out, only the team leader (usually) sees the exposition text blocks, so the general plot of a TF/SF needs to be straightforward enough for people to get the gist of it simply by following along. Penny Yin is pretty much the gold standard where this is concerned; pretty much anyone capable of navigating from one end of a mission map to the other can figure out what's going on. On the opposite end you have stuff like Lady Grey - ok, we can infer from the NPC giving the missions that the Rikti are up to something, but why the blueberry fuck are we taking on 2/3rds of the enemy groups in the game that scale to level 50?