My problem is that people who become companions tend to get subordinate to the player character. Isabela and Merrill were never on the same level, so they didn't lose. Cassandra was written exceptionally well but even she has a "second rank" aura about her in DAI, as opposed to DA2.
I understand. However, I think that even in that situation, Calpernia fits for the same reason as Cassandra: because they feel more like Darth Vader material than Palpatine material, if you get my analogy. Cool and powerful, but always second to another one, long before they met any PC.
Cassandra was a hero back in the anime movie, but she was always content at being the right hand of someone more powerful, and even in DA2 she became leader of the remaining Seekers only because the actual leader defected. And then a smartass dwarf played her like a fiddle. Calpernia too was only leader of the Venatori because the actual boss said so, and she was left in the dark about her final fate, which can't be said of Samson.
Also, I'd dare to say that Bioware doesn't treat NPCs any better. Sometimes it seems as if they can be derailed even more.