Strong or weak Jet stream

I actually thought this was correct:

Global warming has been used to explain that the Jet Stream would weaken, bringing more extreme weather to the temperate zones.

But I kept seeing a meteorologist saying that this was wrong. Not just any meteorologist, but one of the most cited scientists on global warming. Thanks to the internet, I got to ask him why it was wrong.

Easiest way to illustrate fundamentally flawed perspective of NOAA figure is to recognize it has an unrealistic feedback. If Arctic became cold enough, according to Figure, the Polar Jet would become even more zonal and there would be no interchange of heat between latitudes.

[…]

A strong Polar Jet stream will inevitably break into large latitudinal variations. The stronger the Jet, the greater the horizontal gradient in the tropospheric temperatures. This exchange of heat between high and low latitudes is a fundamental part of the climate system.

That makes sense. The first paragraph easily explains that the figure is wrong.