I would think a mentalist could solo okay.
They can charm pets to get initial aggro, then you can DoT/nuke the mob down.
heal over time should keep aggro on pet, and power over time should cut down med time.
You might struggle in the very early levels before you have access to all these things, but the mentalist does have a lot of tools.
It can help almost anyone level by casting the Heal over Time, which like Devine Intervention, does not draw aggro to the caster, and in PvE, heals sufficiently.
If you go Druid, Nature druid is only viable option to solo...keep enough in nurture to give adequate buffs, but the pet and DoT will be how you kill on a druid.