They do publish numbers in a very hidden page: https://www.xfinity.com/networkmanagement
Edit: You can see these new speeds listed here: https://www.reddit.com/r/Comcast_Xfinity/wiki/knowledgebase/...
If it was comparable to fiber, then they would advertising the upload prominently like fiber ISPs advertise it.
> If you're given the choice between a low bandwidth private connection, or a small share of a larger bandwidth connection, take the small share.
and mostly that is fine because wifi is also involved which will domniate any availability or service quality metrics.
https://en.wikipedia.org/wiki/Statistical_time-division_mult...