Mistakes when playing as Humans.

Let's clarify things. Should a Knight take resistance and deflection against a Warlock?

There's no need to take resistance – overwhelming magic will overwhelm him. But deflection is actually a useful skill, as there's a chance to reflect the spell. After all, it's not necessarily the case that the Warlock will cast Meteor Shower.
In general, neither of these skills will be very helpful against a Warlock... He needs to be destroyed with brute force, as quickly as possible, and it's better to take combat skills.