On iOS they can get away with less RAM than the rest of the market by killing apps, relaunching them fast, and having severely restricted background processes. On Mac they won't have that luxury. At least they have fast SSDs to help with big pagefiles.
With the heterogeneous memory, your 8GB computer doesn't even have its whole 8GB of main system memory.
When the touchbar MBP launched in 2016 people were already complaining that it couldn't spec up to 32GB like the competition. Four years later, and it's still capped at 16GB.
Hopefully they can grow this for next year's models.