I agree with the duration. I think the idea of the set is fine…once the bugs are fixed but it needs to be smoother. My rough changes when doubling the duration would be as follows:
2-Piece Bonus: Gain a Momentum stack when attacking with a Primary skill. Each Momentum stack lasts 4 seconds at a maximum duration of 20 seconds. Your Primary skills deal 8% more damage per stack of Momentum.
4-Piece Bonus: Casting Strafe against enemies will automatically shoot your last used primary skill, and also give 60% damage reduction while strafing and for 5 seconds after. While casting Strafe, you move faster and gain 1% damage reduction per stack of Momentum.
6-Piece Bonus: Your primary skills deal 20000% more damage. Additionally, your primary skills deal 1000% more damage for every stack of Momentum.
The values could be changed of course based on whatever fixes and etc they do and I don’t know if the amounts I put are enough or too much. Basically, I am trying to make it like a burst build, where you stack your Momentum to get really high damage/defense for a few seconds then it slowly drops to a baseline level until you stop and reset.