This part in particular stood out to me.
We aim to achieve feature parity for all versions of Borderlands 3 early in 2020, but for the moment the version of the game that you play on Stadia has benefitted from the updates and fixes that were released through October 24
It's not clear exactly what "early in 2020" means, but if you're playing Borderlands 3 on Stadia in the meantime, you're playing a two month old build, missing many fixes/updates.
I thought a key part of the pitch for Stadia was that you don't have to wait for updates?