They build Trinity Force and rofl-stomp champions who don't build defensive items.
I highly doubt any of them could solo a four-item ADC with nothing but Trinity Force. They would need one or two defensive items to help them survive the ADCs damage and reduce their healing enough that base damage is enough to kill them. They will typically have a level advantage as well, which gives them a significant advantage in base-stats.
And honestly. why wouldn't a four-item ADC die quickly if they didn't bother itemizing for defensive items? If they ADC had Bloodthirster and even a mid-tier defensive item (i.e. Chain Vest, Warden's Mail, Giant's Belt, Negatron Cloak, or Spectre's Cowl) they should be able to survive long enough to kill the enemy or for their team to help them.
If Corki managed to solo a four-item ADC with nothing but Trinity Force, then that four-item ADC screwed up majorly (or they were bursted down by surprise because they are still squishy as heck). If they message up that badly, then they have bigger issues that Trinity Force.