This is partially true; but once again, you are talking rotational (radial) forces/loads that ball bearings were designed for. More/smaller balls = a higher RPM bearing; fewer/larger balls cannot take as high of RPM but because of the larger balls, can take more load. I once was looking for main bearings for my 125 at the bearing supply. They had the right inner/outer race dimensions but had fewer (larger) balls and the guy recommended I not get them because they would not withstand the 10K+ RPM the engine was capable of producing.

Of course, the load vs. RPM considerations mean nothing really in a suspension pivot because there is only oscillating rotation and low frequency. Really, what would be ideal for suspension would be a sealed, full-complement roller bearing; but, alas, they do not exist in diameters samll enough for bicycles and are rarely sealed like cartridge BBs are.