In the screenshot https://i.imgur.com/RH5cgSF.jpg, redstone ore is shown as generating with a peak at the lowest levels of the world.
It doesn't actually generate like this in 21w07a. The actual distribution is flat, with an abundance of about 0.16% (1/600) per stone below Y=12.
How I reproduced this:
I generated a world over a large area (-4096 .. 4095 in x and z) using the seed 1. Then I collated the ores in these 262,144 chunks as a ratio of ore to stone blocks (stone, andesite, diorite, granite and grimstone). I used these collations to produce totals and plotted them on a chart.
https://bugs.mojang.com/secure/attachment/381319/ores%2021w07a.png
The ores behaved as expected except for redstone ore. Iron, emerald and coal cannot be clearly verified above Y=120 due to insufficient data.