@BloodyKyona Solo divide is mostly about knowing what to do and not too much of being the best on the class. For example,
Supply missions, you just run around ignoring all the mobs and get an S rank
Search & Destroy, is pretty much the same but you also attack the mobs with a blue glow and ignore the rest
On Boss fights, you ignore the boss and just kill the little mobs until you kill like 3 or 4 and get an attack buff that destroys the boss
Free-for-All is pretty much grouping as many exploding mobs together or make them explode 1 by 1 on the non-explosive mobs.
The playstyle is kind of different so maybe that's why some people think it's harder.
Going by what has been said only the "Big Boss Stage" at the end seems to be the problem where there are no "little mobs to destroy". That being said I don't think that you even need any skill at all to clear these stages as I'm pretty sure that even "something like this" would be sufficent here.