I disagree. I thought SuperS was a decent season. Definetely not in the same league as Sailorstars, but, Takeuchi indicated that, while the S season was about Usagi's growth, SuperS was Chibiusa's season. I don't think that Chibiusa would have been emotionally mature enough to deal with the anti-messiah or witnessing her friends die in a similiar fashion to the final episodes of the Sailorstars season.
Now, for Sailorstars.
There are a lot of reasons why Sailorstars will likely never air in the US....the Three Lights, the return of Uranus/Neptune(although they returned in a special during the SuperS season) and, of course, the licensing fees. However, Sailorstars is a very violent season. Even during the first few episodes, Usagi really goes through a lot of nasty things. Her man is taken away from her and in a plot reminiscent of "Sleeping Beauty", Usagi has to pursue him through a maze of prickly thorns. Since I don't want to spoil it for you, I'll try to stay away from some of the other examples of the suffering that Usagi experiences throughout this season.