Ni-Mh batteries, low capacity better performance?
There's more difference between cells than good or bad quality. Cells can be built to have good energy density (store a lot of energy) or have good power density (drive a lot of output current). 

Unfortunately the tweaks to the structure required to improve one generally worsen the other. An energy cell will have a lot of fine structure to give a lot of surface area to the electrodes. A power cell will require robust electrodes with large area conductors back to the terminals, which take up volume that could otherwise be storing energy.

This applies to all chemistries of cells, not just NiMH. It's especially visible if you browse lithium cells, as they are specified for discharge performance, modellers are interested in whether a cell can deliver 20C or 65C safely. An AA cell, because it has button terminals, cannot support a very high current. A power cell has to be soldered in, or at least connected with a special connector. This means that readily available (AA size) NiMH cells are designed for low current applications like torches and cameras, where an energy cell is appropriate. It's a quirk of history and the market that NiMH power cells tend to be built into appliances by the manufacturer, and so the power cell versions are very difficult to find on the open market.