It is a very confusing issue, but in reality the load is not there for the benefit of the cartridge, its there for the preamp.
If the preamp is stable, it won't be bright even without a load (just the internal load of the phono section, which will be 47,000 ohms).
The gain has nothing to do with loading; 66 db is a good amount to allow you to work with phono cartridges of as little as 0.2mV.
If you want to get into the math of it I can point you to some links, but the bottom line is that you are better off with a phono section that does not require loading to sound right. When the loading is present, the cartridge has to be able to drive it- and the energy has to come from somewhere, which is the cantilever of the cartridge. It gets harder to move as a result, which means its not going to extract information from the groove as well.
So a stable phono section is important!