Why Erenville succeeded as a character where others did not

[Cleretic]

I've said several times, the reason Erenville was 'squandered' is because he's literally just not built for the spotlight. Characters are built for purpose, and Erenville's purpose is to be a minor character that gives us actionable information that he doesn't use. He's designed for that role, being very passive and introspective, and having skillsets that at best tangentially lead to progress, because he's designed to be far on the sideline. Hell, the game actually gave him the spotlight for half a zone, and he used it to get us to pick up poop; he's really not a good pick for a lead role. Which is the main problem with the structure the OP likes; not every character can actually shoulder being 'main character material'.

Krile's got the same problem from a different root. She's designed to be a constant 'support contact', similar to a lot of the O.G. Scions, so she's more intended to give us busywork that actually does progress the plot, but doesn't itself have to be the 'spotlight' moment. That inevitably does mean that in Dawntrail she isn't well-suited for the spotlight either, but she made the most of what she could get. Her main difference to Erenville is that she actually did get a storyline that played to her strengths: Stormblood Eureka. She's actually very well-suited for a mystery like that, it gives her a lot of dots to connect, info to dump and objectives to come up with. That works really well in side-content, but when they played the same general playbook in the MSQ it's just inevitably quieter than a much bigger story with more defined setpieces.

And I know that none of you want the sort of overhaul required to be able to make a character unsuited for the protagonist role fit for it, because they did that once, and most of the community decided she was the worst part of Stormblood.