Anything Magic Damage

Why has this game become anti-magic damage/ap? I swear laning phase level 4, opponent mid-laner just goes back and buys a mercury tread for so cheap and you literally end up doing like no damage. Then they buy a hexdrinker (also cheap as hell) and now, thanks to like 2000 gold, you will literally not be able to kill their mid laner ever again. It'd be nice if AP mages can just buy 1 item for like 1000 gold and literally take 0 damage from all AD sources, but too bad we can't because we have other things to buy such as mana/mana regen/AP. Late game, it seems that literally everyone that's not an ADC or an AP mid champion ends up with like 4000 health and like 200 MR from like 1 item and you cant even tickle them cuz they'll kill you so fast with their 0 damage items...

TL;DR, Top laners/junglers build like full tank, ends up dealing more damage than AP mages who build full damage and magic pen. Even squishies can just build 1 or 2 MR items (which are cheap as hell and dont even mess up their build cuz they dont have to worry about buying mana or anything) and they end up taking like no damage either. APs are literally useless, except for your mainstream AP champs (which, sorry, but I don't want to pick from a pool of like 3 champions).

Solution? Well let's make it even! Why not give AP mages an exclusive item that gives 500 Armor and 3000 HP that costs like 500 gold! :^))))))))) Now junglers and tanks will know what it feels like! :^))))))) ffs...