As Ptr_Grifin pointed out elsewhere though neither of them are likely full-powered Juggernauts.
"According to New Excalibur, when a Juggernaut becomes apostate, another Juggernaut is selected, but neither are at full power. They are in a weakened state so that one can prove himself and kill the other to claim the full power."
Likewise Cain's durabilty/power was reduced when he shared his power with Black Tom too.
It will be interesting to see how it plays out however. Since Kuurth still lives are they only (possibly) still at half a Juggernaut (Colossus + Jug/2 & Kuurth + Jug/2) each? Apparently Cain's killed at least one other potential usurper on his way to reclaiming the Ruby during his days with Excalibur. That would explain their casually breaking bones.
Largely I agree with Pr's interpretation though.