One thing that FASST receivers have really are more like 2 receivers in one, each with its own antenna, as well as a system that anticipates what the next logical combination of commands should be in the relation to the last one received, like it knows that if you are with the ailerons at full right, then it knows that a splitsecond after it can't be on full left because you have not had time basically to get to that position without passing though the rest of the proportional part with their respective signals sent. So if the FASST receiver receives another signal that happens to cause interference due to saturation like at a large flying event, it will first analyse orientation and strength in comparison with the last true signal received, then decide on what the data is actually telling it, and which is most likely to be the real signal, even if it is the weaker one. I guess you can compare it to a fly by wire system where you are flying with an "in between" computer rather than direct. But Futaba is not the only ones to use this type os safety system, as Multiplex have been using it from way back in the 35mhz days of the early 80's, and back then were considered one of the safest alternatives there was, even with 2 radios on the same channel, but Futaba just added it as an extra safety precaution in an attempt to make the best they could. The FASST system was originally developed for industrial applications like the big construction cranes which obviously can't be allowed to just drop their cargo on top of passing by pedestrians, and so has to be resilient to interference. There are other companies that are making the FASST compatible receivers, he best alternatives actually being made by FrSky, although Orange also make them along with a number of other companies.
Another thing, if we are talking Futaba Vs. Spektrum rather than S-FHSS/FASST vs. DSM2/DSMX, I have one thing to say: S-Bus!