ADS Sensitivity is not the same on all Guns

I ADS alot, even mid-close range with AR and SMG's, i always wondered why is it so hard for me to track people with my aim in Apex Legends, compared to other games. I do notice the ADS difference when i empty my primary weapon's magazine and switch to the secondary, that's when i have trouble connecting the shots and i tend to overaim, not being able to finish a near death target. My FOV setting is 100. Mouse DPI is 500 and in-game sensitivity is 1.8. I'm no Shroud or any pro, but i was always good at FPS games because they're my favourite genre, but i feel gunfights in Apex are never in my favor and it feels like almost every player i face has better gun skills than me. I don't believe it, something else might be wrong, it can't be this way, i should have been used to gunfights til now as i played since launch. I'm not throwing myself into gunfights with half HP or anything, not picking fights that i know i am at a disadvantage, like position or equipment/weapon, i always had great situational awareness, but the gunfights in this game feel so sluggish for me, aiming feels sluggish, i never had so much trouble aiming, especially in a FPS game. I'm still trying to find out why and how to improve on it or if it's just something that doesn't tick for me. My hardware is good, no problems on that end at all.