In Book 1 it was unclear if portals were guarded, Parson was shown with many mages ready to shoot him.
Yes and no. We don't know what kind of time passed in the MK to bring the mages out to threaten Parson.
In Book 2 we have scene where portals do not appear to be guarded which reduces chance of portal conspiracy, but...
Indeed. Will you assume that portals are always guarded when we've seen then not guarded? Will you assume that there is some kind of portal guardian force which kills all interlopers into the MK who are not casters, when there is no logical reason as to why such a force should exist?
"Yes and no. We don't know what kind of time passed" - Thus I said unclear.
"Will you assume that portals are always guarded" I am not assuming anything, just saying what is still a chance (with help of predictomacers). The chance has reduced with book 2.
"when there is no logical reason as to why such a force should exist?" I think you are assuming here on no logical reason. If portals allowed non-mages to go through
then big risk of warzone and no sanctuary for neutral mages. Thus a myth to keep others out may make sense and such a myth would need protection.