The Gunbreaker AF gear's dye maps are disappointing.

[Mouthbone]

Also, "there are a lot of red accents, that's why they left the gradient" is my point as to why it feels lazy -- in fact, if there are a lot of red accents, isn't that more justification for why all of the red elements should be dyable instead of just the collar?

This would just create a different issue, now you would be stuck with a white collar
There are 3 main colors in the set: black, red and white. Black and white cover the most/least of the set - this is why they chose those 2 colors
This is just a limitation of the two dye system and the design choices
I do understand the issue and I agree that they could have designed the gear to better fit the 2 dye channel system, but I feel like this is something that can be worked around