Playing anything besides a tank top lane vs an AP opponent is the worst

Because even if you snowball if the enemy bot snowballs you are still irrelevant. Your lack of armor (because you had to itemize MR instead of armor early on) means you get shredded as soon as the enemy bot lane comes near you. At least the health that comes with armor is usually enough to give you a somewhat equal chance against a AP opponent who snowballed but not against an ADC who has shields and peel to make sure you die before you ever get near the adc.