They are not uncommon at all. I have discovered with the help of many great guitarists that for ---at least a large proportion of finger types--- the ideal shape (for the i, m) is short and asymmetric like this:
I could say that the picture has it a bit longer than I like to have and the fin does not "fade off" as smoothly and curvy as I want it. The main reason I let longer nails is durability. For instance, say I want to do irrelevant work like home reparations, or commit to a season of heavy practicing (scales, etc...). In fact, with this shape having longer nails makes the right hand "nail fin" flap sort-of-speak making the sound less robust/rich.
In general, I try to optimize the sound quality given the required durability constraints --- it's a trial and error process and takes some time to learn.
For concerts, I only care about the best sound.
You can experiment with different sizes and shapes, nails grow. Stroke motions and contact surface smoothness certainly influence how fast nail degrade; imagine that if the contact points are not smooth enough (in a microscopic level), they will degrade faster.
Strong nails are also related to the diet quality. Also try perhaps some kind of treatment like olive oil --- web is full of suggestions, just use common sense. Last, note that whenever I had to use fake nails (like with very thin fabric sheets and glue/retin) my own nail became weaker after I removed it.
Last, take a look at Scott Tenant; Roland Dyens was also having similar nails.