A sincere question, why Tiamat was nerfed to begin with?
I don't recall people seeing
as a problem. While it could give free waveclear to many champions, this item honestly wasn't THAT useful outside of this, unless you upgraded it into Ravenous Hydra in which the case it gave lifesteal and a lot of raw AD. But not all champions completed Hydra first; many champions would rush Tiamat just for the waveclear and finish it only later in the game, purchasing other more useful items first. Lots of champions, however, still preferred the raw power from rushing The Brutalizer.
Some champions that used this item were problematic, but the problem wasn't on Tiamat, but on the champions themselves. Examples include Fiora, Darius, and Kha'Zix.
Nerfing Tiamat only served to cripple champions like Fiora and Kha'Zix who are either forced to rush Hydra (thus delaying other useful items such as armor penetration items) or spend a long time in the game without waveclear. In addition, thanks to Ravenous Hydra being much more expensive, rushing it is a pain when you are behind.