You're not the only one having a hard time aiming in this game. Most weapons in Apex has a different ADS sensitivity, and adding and removing sights also changes the sensitivity. Check my profile for a few posts about the issue. Worried why so few people are not reckoning this as a problem.
To sum things up the RE-45 seem to have a 1 ratio but the longbow has a 1.4 ratio. So unless you pick up the same weapon every round its near impossible to build any sort of muscle memory to speak of.
Unless Respawn gives us the ability to change ads sensitivity on all zoom levels and give us the option to force chosen FoV during ADS, your only option is to use one weapon with the same optics every round, then mess with the ADS ratio to match your sensitivity.