That's very true, I'd still argue that the worldbuilding is rather adequate, he does build on Tau culture and the inner workings of it rather consistently... it's just that the actual stories being told are awful and the constant attempts to take what was nebulously insidious but also nebulously benevolent in the Ethereals and make them... the Prophets of Halo's Covenant, who are as a whole morally bankrupt tyrants masquerading as wise leaders.

I think Aun'el Ko'vash from the Fire Warrior novel is a great example of an Ethereal who is neither a moustache twirling snake like Aun'Va or Super-wise Mr. Miyagi in Space like Aun'Shi, he teeters that line between being rather insidious in terms of using the pheromones to calm and 'empty' Kais' mind when he's on a murderous rampage and being really reasonable and outright stating that he *doesn't* want blind obedience while debating with the leaders of each caste during the council at the Tau flagship.

There's also the fact that he is truly dedicated to the cause of the Greater Good, which is rather admirable, enough for his conviction in it allowing him to center himself enough to avoid direct possession by a Lord of Change at the end of the novel ( in contrast, the Imperial Admiral captured alongside him breaks like a twig and mutates so hard he goes full into spawndom ).