I'm only rank 14 THM and CON, and from what I can tell so far, both caster classes are quite strong in the solo department. As mentioned previously, it is certainly worthwhile to spend a bit of time doing some crafting, as the physical experience gained is very high (like 1k per synth).
With higher base stats, particularly in VIT and MND, you can hold your own against some pretty tough mobs. I was doing Dodos in the Drybone area at rank 9, and have been doing Aldgoats near Bloodshore at rank 14 (phys. level 26).
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