Well it's a little bit of both being a problem. Mostly Lucian though yeah.
BC on ADC was super niche last season when we still had old LW. And all the while it costed 3500g; way more than armor powerspikes. I'm guessing BC was supposed to cost that much maybe because it was meant to be a later game item for fighters. The problem with BC strong as a first item is it counters armor and continues to scale itself up with your damage and your opponent's defenses and almost makes the user target agnostic.
Full tanks have been overbearing all season before we decided to bring back BC as relief. But it still has its old problems.
This season though ADCs had to have used
. Buying this item while often necessary is a sour pill to swallow as it's limited effectiveness attacking carries. Comparitively BC becomes much more attractive to ADCs now that the old generally broken LW is gone. Especially on Lucian who abuses BC unfairly well with his ult, passive and CDR wants.
A possible solution is to put more crit interaction into Lucian's kit but nerf the base effectiveness. Make Lucian's ult crit like MF's? Not sure if it truly solves the problem but for the most part I'm only annoyed with both Lucian with BC. I'm fine with melee characters & Gnar building BC.