I gotta say that the "pretender is raising an army" events are pretty awful to deal with, though I didn't know that giving them land would actually avoid that. (and for me they tend to take years before they actually announce war) If the ruler doesn't have around 18 Martial and a demease of 7 or more, generally the ruler is going to lose, badly.
I've noticed Decadence wars to be even worse though. I once saw the Abbasids completely floored by a 180,000k doomstack of troops in the 867 start because they were at 100% decadence. Are decadence wars naturally that dangerous or does it depend on size? (cause the Abbasids held both Spain and the Arabian Empire before it fell apart)