Are you confirming that the troop rotations are not random? If so, this would be new and would have been a VERY exciting patch note.
If not, then your statement is false because of the nature of random numbers. “Certain” is not true. “Probable” is true. You believe it’s improbable that Infernus won’t show up within 6 weeks. The Pharos-Ra thread that ended with the devs forcing Pharos-Ra into Soulforge as a Christmas gift is evidence it isn’t true. That thread also contains a promise that the previous paragraph’s “the troops rotate” is a planned change to the Soulforge.
In short: I’m really excited for when this bit of information resurfaces (Yes, I keep the link on speed-dial because I’m so excited for when it happens):
I think the way you describe Soulforge is how it should work, but unless there’s been a ninja patch that is not how Nimhain explained it to us.