How can you call the two most popular cartridges on the market "under rated"? Under rated indicates it's use is waining or never reached full potential or it never really "caught on".
There are several under rated cartridges sitting in the shadows of the limelighted .223 and less so .308.
Right now, you have people adamantly proclaiming the .223 is a magical dragon slayer out of all proportion to it's size or energy level. Truthfully, I had one in the early 80's and found it severely lacking as a coyote killer. I owned two different .223 rifles and traded both away simply due to lack of killing effect. As proven later, this was basically the result of failed bullet design/performance but still, this was my perception of the little popper.
Regarding the .308, keep in mind it was AN ATTEMPT TO APPROXIMATE 30/006 performance in a shorter cartridge. Recheck that "attempt to approximate" remark. Although the .308 is a versatile decently powerfull cartridge, it was, is, and will never be quite as powerful as the best 30/06 loads.
Just my thoughts on your topic. The cartridges aren't really "under rated". They're just better than the worst but not as good as the best.