Character agency isn't just about making decision, even more in a RPG game with a linear story. It's also either being the key for the story to progress (that's why Zero have a lot of agency during 6.x) or that it's logical for the character to do what it do. There isn't any of that in Dawntrail, while it's present for any story before.
"Lore wise", the WoL isn't going with the flow during Heavensward. They are doing what they do because they want to, to repay House Fortemps kindness, same for Stormblood, the war is inevitable, this make no sense for the WoL not to take part (even more when you think that due to the Griffin, the WoL may think themself part responsible).
After realising that only they could beat Zenos, they become the key element of the story, without the WoL, there isn't any way for the story to progress in any positive way.
Won't even start with Shadowbringer and Endwalker.
And Heavensward isn't a "right place, right time". The war was supposed to be an "eternal suffering" for Ishgardian, it's the WoL and it's companion that created the situation for peace and the fall of Niddhog.
To be more clear : even if it's a game where we make no decision by design, narratively the WoL isn't a pushover... until Dawntrail.