the fact that it was orc poison that killed her does at least make sense from a Watsonian perspective

That is true, though I will say that if they recast Adar, why not Bronwyn? But if they didn't kill her off solely to regress Theo and his relationship with Arondir, that does mollify me.

Re: Disa, I saw it more the passing of time cooling her anger since months have passed since the last time we saw them back in S1, especially since it was clear Durin III regretted his hasty words but both he and his son were too stubborn to fix it.

Point taken, that's plausible.