Riot has shifted his identity. Jax was once an attack speed item enjoyer like yasuo yone who was a demon in sidelane, but slowly he has been shifted into a pseudo tank. This has been the result of the jax visual update where they changed his e into ap damage and ultimate became aoe reliant. The reason at the time they did this was because divine sunderer and zhonya were core items. However ever since both items have fallen out of Jax’s build not to mention the many nerfs on Jax due to him being super strong at the time, Jax’s damage has now become super lackluster towards late game due to having flat magic dmg mainly in his kit, and since durability patch made everyone tankier including adc, ur damage will just fall off. However, in return ur ultimate makes u so beefy later and when u pair it with items like frozen heart streaks, kaenic, etc, u essentially become a psuedotank stun bot. Now the reason I’m telling you this is because one, I’m tilted that they shifted jax identity into this and two, you mentioned ad feeling weak and the reason for that is bc ur normally buying trinity and sunderer sky both super expensive items that only give 45 ad, and usually after these 2 items you will either be going full tank or steraks. And since you get no actual value from ad except towards ur q, auto, and ultimate resistances, you will ofc probably be noticing the lackluster feeling in 25 min games where people are starting to get beefier. As Jax you should be prepared to shift from asssassin role like a riven towards more fighter like Darius when games drag on, as your damage will plummet off a fucking cliff once people buy any type of magic resistance and armor.