ah ya the age old pinion head size debate. its been beat to death since time began. alot of bad info and urban legend out there. plenty of well qaulified experts certainly wouldnt agree with your statement. theres alot of variables when comparing one gear set to another
just one of probly thousands of bits of info
Its sort of complicated to pick the best ratio based on strength. In the end, they are all acceptable designs per the manufacturer, or they wouldn't make them, and the better the quality of that manufacturer, the better the quality of the gears for which you will pay more.
The thing to remember is the ring gear diameter is constant; it never changes. Because of this, no matter how many teeth are on the pinion, the mean diameter of the pinion will always be smaller than the next numerically lower gear set for the same model axle. Because the ring gear diameter is constant, to get a lower gear ratio with the same number of teeth on the pinion, they must place more teeth in the same mean circumference on the ring gear, which makes the size of the teeth smaller, and therefore their contact area smaller. At some point, the designers feel the teeth on the ring gear are getting too small for sufficient contact, so they reduce the number of teeth on the pinion so they can reduce the number of teeth on the ring gear. Since the mean diameter of the pinion is selective, they are at liberty to make the tooth depth as deep as the pitch will allow, thus keeping the pinion teeth relatively strong. As was stated, the lower the gear ratio, the less force that is realized by the pinion under the same set of circumstances, but the actual strength of the pinion gear due to its smaller diameter versus how much less force it sees is the variable that needs to be determined. The other thing to off-set these factors is actual strength of the gear teeth based on pressure as determined by the actual contact area and how much of how many teeth it can be spread across as it turns. This pressure increases per square inch as the number of teeth on the ring gear increase due to the ring gear teeth getting smaller, regardless of pinion diameter, tooth depth or number of pinion teeth. Its the actual size of the ring gear teeth that determine how large and at what pitch their contact area can be, which I'm sure is used to its maximum by the gear's design