So far, I have had almost no fun running any skirmishes in groups. The scaling is ridiculous.
Solo seems balanced for you to level your soldier alone. You would not have much trouble running them without your soldier out. The bosses drop easily, and I face harder fights in normal quests. Move up to small fellowships, and the repetitive fights are still trivial, even more so given that some of the fights are against two normal enemies. The encounters are also easy, although some of the lieutenants are fairly absurd (exploding for most of a squishy’s health). Then the boss appears, and that fight seems to be balanced for a full group of six, on the assumptions that all your soldiers are leveled fully and that your group learned to coordinate well despite never needing to before that one fight. Even that would not be a problem were it not for the suicidal NPCs that do not seem much tougher when you have a group going. Beating everything in a skirmish is not bad, but the NPCs actively run into fire auras, shadow DoTs on the ground, and anything else that can hurt them, while wanting to tank.
I feel as though I am forced to solo enough skirmishes to level up my soldier to my level, and then only join groups with others that have done so. In six to eight months, this part will be a smaller problem, when most main characters have decent soldiers, although alts will continue to be suicide in group skirmishes. Until I am willing to put in that time on every character I play, and ruthlessly kick anyone who has not, any group skirmish seems like a huge waste of time. It takes 30-40 minutes to test that because the very last fight is the only challenging one. That would be less annoying if you could re-try that fight after seeing what went wrong, but the NPC dies, so you fail and must start over. Putting a half-hour of grinding trivial trash between every re-attempt is a problem. More than half your marks come from clearing the last fight and getting the daily bonus; why risk getting only a third of the full reward in a group when you can consistently get the whole thing solo?
It is a worse situation than the normal problem of needing your friends to level to the cap before you can play with them. Not only may your characters have a level difference, so do your soldiers, and you all need to level your soldiers solo unless you are happy losing at the end and only getting 1/3 of the reward when you play together. Even if you are the one at the cap waiting for your friends, you still need to solo grind to bring up your soldier.
I joined a group for the raid-sized Siege of Gondamon skirmish. The last fight was turned up to three arch-nemesis class enemies, two of which had fiery damage auras. Conveniently for our raid, one of the flaming dragons went into anti-exploit mode despite fighting on a flat surface, so we took down the other and the boss. When it exited anti-exploit mode, it reset into drama mode and never exited, so the raid just stared at an un-attackable enemy until everyone quit.