[throwuwu]

On a tidally locked planet the polar region is effectively the terminator line. There is also a greatly reduced Coriolis effect due to the very slow rotation. The insolation of the day side is a lot higher as mentioned in the article and is continuous rather than intermittent. All of that would lead to increased convection. Imagine the difference between a kettle being heated on a burner vs a kettle being heated by a blowtorch that rotates around it. The behaviour of the fluid in each will be quite different. Not a perfect model by any stretch of the imagination but maybe more intuitive.

[lostmsu]

IMHO, with kettles as you described variability of temperatures with rotating blowtorch will be lower. I don't think convection will be much different between two cases.