Intelligence is not a physical property, it's an information property. It's built out of time, not any physical stuff. It's software, not hardware. And increases in intelligence also increase the efficiency with which the agent gathers information... so even if the sensory bandwidth of the input devices is declining, the perceptual bandwidth can be increasing.

Of course eventually you start running up against mechanical limits and you decline. But that peak is much later than the peak in sensory bandwidth.