We got the rest of the Beforan ancestors and, I CALLED IT!!!

Sollux is The Helpsmam, of the following description:

A key part of Beforan society is emphasis on voluntary service, by using special abilities to assist with public works and infrastructure, like healthcare, energy production and such. Certain members of this force of volunteers are called "helpsmen", so that's his title. He's extremely enthusiastic about putting time in the power plant, using his telekinesis powers to boost the electric grid. He spends hours or sometimes days on end clutching the terminals with a huge smile on his face, thinking about the joy he is bringing to every troll enjoying his electricity. At some point due to a karmic chain of events, there is an accident that affected him quite negatively, but we don't need to talk about that.

This has nothing to do with knowledge. Meanwhile, this is Terezi's:

The Songbird is also a sort of helpsman, using her abilities to help with coal mining. Due to her great sense of smell, she played the role of a mine's "songbird", which is similar to the way canaries are used on Earth. A canary is brought deep in the mine, and if it stops singing and dies, that means there's too much gas and people need to evacuate. She uses her nose to detect gas, but an injury which started this karmic chain of events left her without a sense of smell, but she tried to keep songbirding anyway. When the Imposter allowed a massive buildup of gas, she couldn't detect it, and a huge explosion followed, rocking the neighborhood above, affecting a nearby powerplant manned by the Helpsman, a tree village housing the Rankmaid and Treeboo, and a hospital where the Lamplady was on her shift. The Songbird lost an arm and an eye in the blast, with the damage to her eye being done by a very specific piece of shrapnel... a stray coin in the mine. She decided to use it as an eyepatch so she could never forget her deadly mistake.

Note how Terezi's tale is all about her knowledge and learning - something notably absent from Sollux's, and notably present in Kanaya's. This further reinforces the idea that Mage is not a knowledge class and Sylph is.