When Zilean is buying Ardent Censor...

+20% AS and +20 on hit dmg early is still a great buff to be honest, not to forget that the stats the Item gives by itself already make it an attractive first buy for most enchanters.

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Quick history: When Ardent Censer became a problem, it provided attack speed, on-hit damage and healing, and scaled with level.

In patch 7.17 they nerfed Ardent Censer by removing the scaling.

After worlds patch, they swapped nerfs by reintroducing the scaling but removing the healing.

The big thing here is that the new iteration is not nearly as strong as an early buy since 1/3 of its passive is gone. People are still rushing Ardent Censer because "they're doing it in worlds so it must be good" not realizing that a big part of the reason to buy Ardent early is gone.

Current Ardent might be just as strong, but it's in a niche for aggressive enchanter supports and has late-game strength versus being a huge earlygame stat steroid for the adc.

Your history misses the most important part:

The new Ardent Censer (post worlds) now gives the support the AS and on hit damage as well as the target of healing. This is a function it has never had before. So they removed the healing but doubled the damage.

Riot should have just removed both the scaling and the healing. Also nerfed ADC itemization which had so much synergy with it, perhaps by making Zeal items unique (in that you can't buy two), and making Warlord's Bloodlust mutually exclusive with Shiv and RFC. Maybe also increasing IE's combine cost to be on par with Deathcap's (1265)