If you want build diversity, stop balancing champions around the items they abuse the hardest.

With the upcoming ADC item overhaul I am almost certain there are gonna be cases where certain champions will emerge as absolutely fucking bonkers because of their disproportionate synergy with one of the new items. Every single time this has happened it seems the balance team focuses on either enhancing a weakness, or just knocking down the champion's overall effectiveness. If a champion is broken with one item and balanced with everything else, these nerfs end up making the champion okay with that one item and dogshit with everything else. The end result is that the champion becomes totally dependent on that item to function. I'm sure everyone who has been playing League for more than 2 seasons can name at least 5 instances off the top of their head where this happened in a spectacular fashion. If you're not going to allow a champion to be effective without a specific set of designated items, why even give players the illusion of choice that a shop provides in the first place?

I get the feeling that some members of the balance team don't even seem to see a lack of build diversity as a problem. It even seems like they had until now been encouraging it by forcing mages to buy a Lost Chapter upgrade and ADCs to buy a Zeal upgrade every goddamn game.