Redstone updates are much slower when many components such as redstone wire, repeaters, and torches are loaded at one time. This causes redstone circuits to in turn run slower than they should. Interestingly, even small isolated circuits are impacted especially when changes in  solid blocks are involved. The amount of delay also seems to increase with the amount of redstone loaded, even when those components are not being changed.

In the video attached, a redstone clock powering a lamp is used to demonstrate the change in tick speed when a block is placed on the sticky piston head. Because this particular behavior is difficult to reproduce, as hundreds of thousands of redstone components are needed to produce notable effect, a world save is included as well.

To conclude, perhaps the massive structures are being involved in each redstone update, and therefore possibly all redstone loaded, since even though the circuits (the clock with the lamp, the sticky piston, and computer) are isolated and independent from each other, the speed at which their states are updated seems to be impacted by activating the piston circuit.