Arandor
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might be a bit off-topic, but I don't think it's necessary to create a new thread (there's already enough chatter).
I think the least useful skills are:
navigation (there aren't many maps with a lot of water, and if it's random, I don't even play with water),
healing tent (if it could resurrect, that would be different)...
ballista isn't very useful either (don't confuse it with a catapult),
tactics aren't very useful either, but they can be helpful against strong enemies...
scouting (there are artifacts, and it's not really needed anyway)
mysticism (there are wells or artifacts for that too)
I don't think I forgot anything...