Scopes improve the aim of all attacks made with the weapon you attach it to, while “Perception” personal combat sims grant flat aim to everything the soldier does. Aim is one of the most important stats for your soldiers to develop, and while it grows naturally as they gain promotions, there’s plenty of other ways to bolster it.
There’s a lot of upgrades and attachments to use in XCOM 2 that increase all sorts of important stats, but in general, one truth should guide your focus-you can’t kill them if you don’t hit them.
