If we assume that an attachment increases the aiming skill, this increase is variable since it depends on the current level we have.
For example, you are level 30 in Laser Sniper (Hit), you add a Laser which gives you +22%, we can guess that you become level 36.6, so the increase is +6.6 here. It imprves your eco since your MinDmg and your HA are higher.
(I don't speak about people with Level 100
)
If you use non SIB weapon, it is fine, but we have to consider the decay, which is NOT variable, I mean you will have to pay the extra milli-pecs whatever your level is.
And according to some old calculations I made for me, decay was higher than the skill gains for most of the Scopes and for some Lasers, which are better eco.
If someone is willing to make such calculations, it would be great to know, for each Laser / Scope (according to their SkillMod + Decay), at what Hit Level they become eco...
Regards,
Xor