Google assistant design is done from Google side, rom cannot do anything about it. About tap to wake this post pretty much explains that.
For me it is working perfectly from the lockscreen. Try deleting earlier saved face data and re-enabling with new face data. Attached screen record for your reference.
Then there is this option under face unlock settings. It omly allows you to swipe 1st and then unlock using your face. The earlier option to skip lockscreen seems to be removed in this build.
I used the other option...was so cool
Actually, after the OTA got downloaded and installed, it showed a pop-up with reboot button.
Have you put the zip file in your platform tools folder.