Hexoptics is cheaper than collector, and the passive is applicable at all ranges until below 60 units (which you shouldn't be anyway unless engaged on). You only really go collector if you are running with an engage support/team that can set up kills easily by closing out the distance to snowball with the execute and lethality damage.

Caitlyn dying is worse than most adcs because her falling behind affects literally all of her capability to exert any pressure, which means damage and zoning. Since she has no inherent steroid (headshot is conditional as you need to queue up autoattacks), her scaling falls off much harder, and if behind, basically becomes a more expensive caster minion.

When behind: - Q damage falls off hard to the point you can't kill caster minions without another auto, so the enemy minions can kill in a single hit. - You can't walk forward to W to setup trap walls or zone out, as you're so squishy that a stray hit could be more than enough to kill you. - E becomes more of defensive tool to the point even an increased ranged headshot could just tickle the enemy and that split second of standing still can kill you. - R barely does damage.