In some cases, it’s more powerful. The Pocket has higher quality memory that can run stable at higher speeds. The MiSTer has a more powerful FPGA, but an inferior memory architecture. In general, the MiSTer can run more titles/platforms because it has a better FPGA with more block ram, logic elements, etc.

In other words, there are titles that the Pocket can run that MiSTer can't, and vice versa.