“Know” seems subjective.
Here’s 3 years of tracking by @jinbatsu. 2019 and 2020 have quite a lot of 10 emblem chests. But I don’t see anything lower than 30 in 2021.
In 2021 there were 8 straight chests without a four star mat. In 2019 18 straight chests came and went witout a 4 star mat.
This is one person’s tracking. But based on those two metrics, it seems like elemental loot has only been buffed sometime between 2019 and 2021.