I agree. Game was fantastic but the ending was a letdown. None of the companions were really at risk of leaving or dying in the end, and your choices made little to no difference in the final battle. Wish we had a better ending, an epic final battle scene where Skyhold is attacked and everyone you've come to know is put at risk. Your choices would affect who lives and who dies, like it did in previous games. That is what the ending should've been.
If Cory succeeded during What Pride Had Wrought, that would've set the stage for the perfect ending. Awaiting an attack at Skyhold and suddenly getting thrown into an epic battle with all of Cory's lackeys would have been amazing, but the ending really consisted of Cory failing and making one final attempt to succeed. He didn't really seem that dangerous after What Pride Had Wrought. Just seemed like an irrelevant madman after that point.
The story was great, don't get me wrong, and the gameplay is fantastic, it's just the ending that needed to be better.
Sera should've been at risk of leaving when you started showing too much favor to the nobles or relying on them too much, and you could convince her to stay, make her angry and end up having her betray you later on or even just leaving depending on your approval rating.
Varric should've been at risk for corruption by red lyrium, I really wish that rumor turned out to be true.
Blackwall is fine as is, Cassandra as well.
Vivienne should've either left or given you the option to kill her if you sided with the mages and gave them freedom.
Cole is fine as is but he should've been at risk for leaving depending on your decisions. Same goes for Iron Bull.