Some attachments like magazines or foregrips could increase or decrease it. And armor/backpacks would reduce it
I think right now ADS movement speed is just directly based off your overall movement speed just scaled down a lot
An example with made up numbers:
100 movement speed compared to 110 would feel noticeably different
But when scaled down 10 speed would barely feel any different than 11. So pretty much all guns feel like the same ADS strafe speed