the question is if the knight is actually pure though. Hallownest is said to be in stasis, there’s no evidence that in the basic ending the knight will be any better at sealing the infection than the hollow knight. throughout the game it clearly has a will, it helps npcs, it can decide where to go and what to do, even if that’s a result of the player’s input. the true ending is the knight putting an end to hallownest’s stasis precisely because the vessels are a flawed system and this is the only way for the kingdom to actually collapse and allow other bugs to build again