The biggest change during season12 preseason was the addition of two new drakes, that of the Hextech and Chemtech drake. While the Hextech drake has been balanced, if not without bugs, from the start, Chemtech is anything but.
When a team obtains the Chemtech Dragon Soul, they receive a buff that grants them a brief second life after they die. This buff is not unlike Sion's passive, with one key difference. Every ability that is off cooldown is available to the champion during this second life, with only some damage reduction applied.
However, in this current meta, where damage is off the charts anyway, how much of a difference does that really make? Especially so when you take into account that souls are usually taken towards the later stages of the game, where everyone has all of their core items purchased, and, more often than not, are level 16 with their ultimate leveled to level 3.
Not to mention, due to the fact that players know they are living on, literally borrowed time, there is no fear of death and will dish out all of the damage that they have, with no regard for their own safety, as none is needed.
Due to all of these factors listed above, as well as the map changes that Chemtech Drake brings, making it easier for the team that is ahead to snowball their advantage and take the Soul anyway, Chemtech Drake soul has reached an incredible win-rate during League of Legends season 12 ranked, and we don't see a way for Riot to nerf it, while keeping the core design intact.