I've been assuming that they stack, but I also would like to know for sure.

Well Evoker is a great skill for your mage character if you dont have many/any shards. Anyways most of the time you get useless skill when leveling up even thou you have slected "Path of Mage", like dexterity, strength and such.. I think they should be more path based. So if you chose  "Path of Mage" you wouldn't get str/dex/const skills/traits to choose from, rather than building "All in one" character, it should be more single path oriented. At the moment all you get is most common skills/traits to choose from a general "common" pool, where as I imagine they should be "path" relevant. So if you chose "path of mage" level up screen should only give you options of choosing from that paths commong/uncommon/rare/unique skill/trait pool. If i make sense here..

That is my impression, too, and if you select warlock and are lucky to get evoker III you get + 250 % spell damage (warlock + path + evoker I - III). This is a huge balancing problem, because without those improvements damage spells are weak and with those improvements they are overpowered. It would be better to:

- Increase the base effect and not the shard effect of spells by 50 %.

- Reduce warlock, path of the mage and evoker I - III to + 25 %.

- Give weapons a - 25 % spell effect modifier.

- Add many caster weapons without the - 25 % modifier and with other effects that improve spellcasting