I think you need more practice at the game because almost every statement there is just wrong.
Bruiser/Fighter items are the only items more expensive than AP items. Half or more of the ADC core of items is below 2700g considering 2x Zeal items, Boots and the Last Whisper choice. Mage items tend to cost more than 3k, with some exceptions and discounting support items. Just because there's AP on Shurelya's for 2100g does not make it a cheap mage item.
Seeker's is the AP item to protect from AD opponents, Hexdrinker is the AD item to protect from AP opponents. One gives Armor and AP but needs to be stacked, the other gives AD, AP and a magic shield and is full effectiveness right away, LOL.
There's only no counterplay when you don't know what to do - that isn't the same thing as zero available counterplay. Figure out what champions do and learn what to do to stop them from doing it.
ANY champion in the game can 2 or 1hit any other champion when the former is fed and the latter is behind. Literally has always been this way. Just yesterday, LL Stylish hit an ADC, as Zed, for over 1600 damage from a single E and an auto attack that crit. No counterplay, LOL.
Most ranged champions have low MR because range is a powerful advantage. Most melee champions have high Armor, HP and MR by comparison because they do not have range advantages. It's a tradeoff, where you're asking for everything handed to you lol.