The illegal organisations planned are indeed very difficult to ascend in - partly this is because in order to hit difficult targets, the assassin must not be suspected - assassination is a 'long game' where assassin characters have to be multi-skilled simply to be able to access the areas where the most likely marks will hang out and get away afterwards. Knocking off a trader down a dark alley is one thing, taking out a guild leader for a town in their heavily defended Guildhouse is entirely different, and can involve a protracted period of infiltration, since assassins are required to leave evidence that it was them that did the job WITHOUT getting caught, and potentially an acrobatic abseil-down-the-walls-and-onto-a-fast-horse escape. Or if they're *really* good, just walking out calmly and unnoticed.
Rogue killing (just like Morrowind / Daggerfall) can incur the wrath of Assassins' guilds - Guild leaders in these types of organisations have a great deal of personal power and have had to work very hard to get it. These roles suit paranoid, ruthless, disciplined players. As you'd expect.
That said, I should point out that almost all the social structures we have allow and to some extent require 'delegation' of tasks for faster advancement - tasks come in faster than you can do them, and you get some reward for having subordinates do the task for you. Each structure is basically its own mini-faction, demanding that you look after the players under you, whilst performing the tasks set by the player(s) above.
