I'd be interested in knowing what the CO2 emissions were from these. You still need to feed the yeast, so you'll have the CO2 emissions involved in growing a crop associated with this. And if you look at the chart in the OP, you'll see that grain production is about half the CO2 emissions of milk. That's likely part of the milk CO2 production accounting.

In addition, you'll need more cleaning/sterilization/mixing. I'd guess that it's lower, but I wonder how much lower.

And then there's the other products that generally get thrown into the mix to make up for things like missing fats. For example, a vegan cheese based on bacteria will often include coconut oil, probably to get the same fat profile.

Whey is an interesting product in general because it's a waste product of cheese making.

It’s likely to be vastly better.

Feed efficiency is critical when doing these calculations as cows inherently need energy to survive not just produce milk. As such even if you use the same crop two different sources of protein can have wildly different levels of CO2 emissions embedded in their creation. https://en.wikipedia.org/wiki/Feed_conversion_ratio