It might be fine for casual users, but it's really not good enough for those using WP to make sites for clients. That said, I wish you the best of success with it, and will continue to evaluate it as you progress.
"correctly per the WordPress specs" - this is like windows rolling out an update that breaks atom, sublime text, and others that were working well. Seriously.
We don't rely on page builders on 100 out of 120 sites. Some sites do have custom themes that incorporated rows for design, which may break with this update.
The sites that did rely on page builders were working great and had no need for Guten.