The author of this Reddit post something interesting when attempting to compare League of Legends to Dota 2:
Pros use the same build 100 games in a row for a reason. Since the game lacks actives and item counters, there are mathematically optimal builds. Stick to the guides if you want to win, no need to try new things.
They further elaborated their thoughts in the pastebin they linked to:
Enemy builds ad/ap -> build armor/magic resistance, and vice versa. This is why most builds divide in two. By optimal build I mean that a machine or excel sheet can determine the right build for you.
A blink dagger is never optimal, since it's entirely dependent on the player to determine if it's worth to waste an item slot and a lot of gold for potentially better positioning. It's not a question of math
That's a strong claim wrt LoL. Is it correct?
My first answer would be: no, while there might be some truth into it, such an claim in its all radicalism is incorrect.
Counterexamples: Do I build Spellthief's upgrades or Ancient Coin upgrades? Do I only build tanky items or do I add some damage output? Do I build DMP for engagement or do I only build tanky items? etc etc
But if pros only build the same over and over, then there's very little I can say to argue: There likely are optimal builds in such a case.
Therefore, do pros build the same over and over? Does LoL feature inflexible, mathematically optimal builds?