To introduce more variations in skill ‘checks’, there are two extra rules:
1) Differing Invoke Values. An Aspect is not worth a flat +2. Instead it is worth +1 if the Aspect technically applies but is kinda dodgy (basically, your free generic +1 without taking up your free generic +1), +3 if it is perfect for the situation, and +2 if it fits.
Dave the Pyromancer is preparing to toss an amazing fireball. So he focuses his will for a Focused Will aspect. When the time comes to launch his fireball, he gets +2 from Focused Will. Or, if Binky the Clown tries to invade Dave’s mind, he can use Focused will for a +2 on his defense.
If, instead, Dave the Pyromancer spends his preparation stage conforming his spirit to the element of flame, for Soul of Fire, that will give him a +3 because it is perfect for fireball tossing. However, against Binky’s attack, I wouldn’t even let him use the aspect. If Dave is really creative and says “I repel Binky’s psychic assault by burning him with my Soul of Fire, forcing him to withdraw,” I will grant that this technically works, but is somewhat tenuous, and give him the +1.
2) Trading Actions for Bonuses. In combat, you may check off a point of Action Stress to give yourself a bonus. The lowest box (since it can be used for everything) gives you +3. The highest box (since it is only useful for one approach) gives you a +1. All others give you a +2.
She-Hulk decides to do a fastball special with Spiderman. She spends her turn hurling Spidey at distant foes, a Forceful approach, giving him a Hurtling Hero boost for his attack. This brings his agility based combat up to a base of Superb for his immediate attack, as he tends to hit with a Quick approach.
The thugs decide they would rather not be hit, but even if their defensive approach is their highest, Spidey beats them by two. So they check off their top action to dodge, and their bottom action for +3, and narrowly escape Spider-smackage at the low, low cost of two actions.
Thus, with these two rules, the success or failure of a given action may often be as mysterious as a roll of the dice.
Fate Diceless is not necessarily less complicated. It is, however, quicker and less complicated to play, as the GM manages most of this behind his screen. And I think, for him, it is no more complicated than Fate Core.