It's funny because despite being an antagonistic force in the film, he had enough screentime depicting his POV that I'd say he also counts as a deuteragonist.
It all depends though and I think it's wrong to say that this won't serve as a definitive suit especially when it's the culmination of the Mk 42-43 and the Mk 45 design principles. Sure it might get more emotional, but that doesn't change the fact that Iron Man's entire character arc took a pivotal change in this film, and it's exactly why so many consider it as a defining part of his character (hence "definitive"). IW may present a new cool suit with emotional moments, but that in no way detracts from how far Civil War managed to actually push Tony's character development far beyond anything we've seen before.
Also "definitive" is relative anyway. What marks as something definitive depends on which aspects of the character you find most appealing and important. Some may still consider the Mk 3 as the most definitive since it was the first red/gold suit, while some might consider the Mk6-7 as the most definitive since it's his first venture as an Avenger.
Personally, I consider the Mk 46 definitive by virtue of Iron Man's key role in Civil War. Its significance feels even more cyclical since the original film designs of Iron Man were inspired from the same era of comics when the Civil War storyline debuted. Also worth noting is how the Civil War comic storyline was notorious for nearly killing Tony Stark's reputation among comic readers during it's run until the first Iron Man film came out where it seemed to redeem his character in many people's eyes.
I don't know if others feel the same way but it's almost like it has come full circle for me when the first Iron Man film came out not long after the Civil War comics, and yet we now have a Civil War film after so much time has passed since that first film.
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