They can teach each other SO MUCH just due to the nature of how both can wield so much aether.

D'lagan exists purely out of spite. His aether is... broken at the best of times. Anything Sath does he shrugs off, so Sath ends up using him as a testing ground for his healing theories. D'lagan benefits over time with getting stronger, Sath becomes an increasingly deadly whm for the trouble. :3

Sitting in the pit of Sath finding D'lagan the most interesting fucked up little adventurer because he can't torture him like he does to other adventurers.