So I think there is some truth to both. A lot of plant material, especially something like alfalfa meal, will break down quicker than most of the minerals and rock dusts in the soil. So this means the available nitrogen can often spike at weird times, which for a seedling or small plant can be too much. And is probably the reason why trying to grow directly in something like that supersoil compost mix would not work at all, and would be too hot. However, a lot of immediately available nitrogen will re-bind into other compounds, or off-gas over the time that the soil is cooking/sitting.
The reason for loading up the soil mix with the compost mix AND all the amendments i added, is to have a wide range of different sources for different nutrients, at different stages of decomposition and availability for the plant.
The supersoil compost mix is made up mostly of slightly different amendments than what I have, that are already partially broken down. This mix was made to be diluted 1:3 to make 75L of final mix. So 125L of final mix leaves me some wiggle room to load up with some more
I did do a little bit of research into what are good amounts of each individual amendment for roughly 125L of soil mix, so I probably wouldn't put any more of the plant material amendments into this much final volume, even without the compost mix in there. But the rock dusts and mineral amendments, I think would be hard to overdo it
One thing to keep in mind though, the pH of the mix will spike and become rather acidic during some of the initial cooking/breakdown process, before settling back around that beautiful 6.8 we are looking for. So you do want to be careful with a sudden high amendment load, as it can turn the soil too "raw" resulting in a fluctuating pH that will of course cause all sorts of issues
That being said, I am by no means an expert or super experienced working with this type of soil (or even with growing cannabis!). So this is a learning experiment. We'll find out in the coming weeks whether or not my assumptions and opinions about this are correct!