Modern processors are designed and optimised for the average user runing an average application. To keep the average user happy, efficiency and performance was sacrificed. Depending on how you see, it are cheating you.

The result that you have will depend on what you are doing and the software you are using, you can be very happy with the results or very pissed of.

HyperThreading is creating a fake core, they are cheating making you believe that you have more cores. Hyperthreading use a part of the CPU that you are not using to run other thread that, of course, doesn't need the part you are using. If this is the case you will have with a lower cost the benefit of a processor with more cores. If is not the case and you are using all the CPU, hyperthreading is useless.

In the rendering example where you assigned a core for a rendering bucket, in theory for a well designed rendering engine with the right schedulling and pipelines there will be nothing left without use in the core. While one part is accessing memory all the arithmetic units are executing data in the pipelines. The core will be runing at full steam and hot temperature and hyperthreading will not work because there is nothing left iddle in the CPU.

On the other hand, if the rendering engine has not an efficient design, most of the time of rendering the bucket is spend calling subroutines and passing parameters and calling again another subroutine and so on, the CPU will have little use with a lot of iddle parts that can be used by hypethreading for doing other things. In this case hyperthreading can be useful.

Stupidity also evolves!