I think you are over-estimating the complexity because you don't understand it. People are building robot hands with lego sets.Because they are a perfect example of something that would be extremely complex needing to be both powerful and delicate and it seems like almost all giant robot outside of battle tech (for the most part) have them. They would need to have a range of motion similar to a human and be able to grip a gun without destroying it, be able to both move quickly and powerfully for grapples, and take a huge amount of force from punching something. And all of that would have to work, all the time, grips too hard and the guns handle breaks, grips too light and the monster gets away, structural integrity of the fist breaks down and the first just gets smashed when it tries to punch.
Yes the hand as a whole is fairly complex, but a single finger is simply a couple of cylinders and proportional or servo valves. The main part of the complexity is going to be in the software and electronic circuitry that controls the valve and coordinates everything, but you aren't doing much maintenance to that.
The fingers are nothing compared to how complex it would be for the robot to maintain it's balance and be able to walk around over uneven terrain.