Differences between a FET multiplexer and regular digital multiplexer?
I revised the illustration to more specifically address your case. In the datasheet for the fast FET MUX you specified, there is literally only one FET per switch, so the only delay of switch pass-through is the RC constant(s) of each FET switch. Worst case calcs shown. Notice the enabling gate drivers are slower as they likely require larger devices and more circuitry to drive and select the switches.


The second datasheet does not give as much insight into the internal circuitry (although it is also FET based - specifically CMOS gate logic), but the propagation delay times are more comparable to the driving logic of the first (on the order of 10nS).  So one possibility is more devices included in the logic switching circuitry of the slower chip. Another possibility  is the process may be faster (lower channel lengths) as they are several years apart. The intrinsic speed of devices scales with process and minimum channel lengths.

Both chips are Digital as they process and pass Digital Signals.