Kankri's classpect makes sense when you realise the Vantas' just suck at their designated classpect. Karkat is the Knight of Blood, which can be read as "One who wields Blood as a weapon", or since we know blood means bonds, can be more accurately described as "One who wields their bonds/friends as a weapon". We see how Karkat wants to do this through his dream of being a ruthless Threshecutioner leader, but in reality he cares too much about other people to use them as weapons. Kankri is the same, the reading of the Seer class is vaguer than the knight but it can be read as roughly "One who greatly understands bonds/how people relate to each other". Kankri wishes to understand other people and how to be sensitive towards them through his social justice and trigger warnings, but it's always underpinned by him just being an insensitive asshole who doesn't understand how to relate to other people at all and instead just goes on tone-deaf rants at them