I am talking about when your level turns X1 and all the trophy and marshal quests change on you. For example, going from being asked to kill Wild Guroks (7-9) at level 10, which is relatively safe, to being asked to kill Forest spider soldiers (13-14) at level 11, which is near suicide, and the others are not much better. Even finding level 10-11 mobs is tough without encountering something much stronger first.
If anything, scale the available trophy/marshal quests based on the mobs average level (Bosses excluded of course) when compared to your current level, and give a buffer zone of +-3 levels. In that case, you would still be able to train on wild gurok for quest XP until level 12, at which point you can handle the spiders and worse.
I find the best XP when not in a group, is killing things just a little below your level. Finding a group for XP is hard to begin with, unless your just looking to blaze and don't care about the XP.