yeah that build looks like solo queue cancer. but literally anyone on earth playing any champ in the game can be strong if they've got a lot of kills and are rotating efficiently
for that build though, its pretty much just cheese. by the time your teammates realise the ez is tankier from the iceborn, hes gotten enough kills to carry and just be strong in general no matter what he builds. the problem isnt buying GA and banshees or whatever in the late game, its that the iceborn can work so well on him and it may aswell act like old vlad sustain with spell vamp + spirit visage. unless your teammates are smart enough to deal with it properly, that builds gonna easily carry him to gold/plat. actually im surprised he didnt get visage with that bloodthirster and the probably vampirism mastery, but he probably had 40% CDR already
i dont like iceborns synergy with ezreal for an ADC, but the item was already nerfed and hes not as popular in the meta so riot probably wont touch him