The number of SEXPs and events used does not necessarily correlate with the length or intensity of the mission.
There is one in SA a specific single fighter needs to be destroyed, but given the fact that I don't know in advance which fighters will be alive at the appropiate point of the mission, I had to set up huge chains of complex events with a descending logical structure utilising multiple variables to keep track of necessary information. All the player sees, however, is one fighter breaking off to pursue a different task than the rest and an directive to destroy Virgo 3 or Aries 2 or whoever it happens to be that is chosen on that particular iteration of the mission. To him, the mission seems relatively simple, and aside from this one aspect of complex logic, it is. But all the SEXPs needed to let the player know who he is supposed to kill caused the mission to max out the Events node limit.
By the way, you might notice that I find the SEXP wrangling to be the most fun part of Fredding. There aren't any really boring parts to Fred---the 24th test flight is about as close as it gets to boring, and even then not really, since it means one is still engaged in part of a creative process and needs to exercise one's mind in hunting down and eliminating any bugs.