Any class can solo in EQ2, it just depends on your ability to learn and play that class, and what you consider successful. You're not going to get exp as fast at lvl 35 as you did at lvl 10 no matter what you do. I've only played the defiler class and I picked it over other healing classes because it was evil, and offered a little more offensive firepower than a true cleric.The defiler's strong points are his group/self buffs, and mob debuffs. At lower levels this allows a defiler to solo quite well if you pick your mobs correctly. At higher levels, they take a back seat to templars/inquisiters for pure healing, but their group buffs and mob debuffs work wonders in raids and high level groups so they are a wonderful compliment to a group with a full on cleric type. I would assume mystics are much the same, but I've not played one.