In reply to Samuel.

Thanks @Samuel for bringing this to our attention. This would be a huge problem for News sites and such...

On performance note, a fresh WP 5.0 RC website, with no plugins is about 0.2 seconds slower than WP 4.9.8, both using the same theme and environment. So having some performance issues is not that big of a surprise, but after reading some of the responses of the github issue you indicated, it is absolutely shocking.

On a sadder note, these people still can't figure out the Columns block to function properly, do you think we have any chance of getting performance issues fixed by 5.0?

Let's get WP 5.0 out as soon as possible, so we can settle the scores, I'm sick and tired to reason with arrogance. In my opinion, at this rate, WP 5.0 will not be ready for at least another 6 months, if not longer. So let's roll out a massively defective product, forget about standards and quality controls. It's only 30+% of the internet, so who cares, right?