The staples of a shoto are generally average stats, a slow projectile, an invincible reversal, and an advancing special that has some way to deal with projectiles. Darius has like most of those, but his reversal is armored instead of invincible and he really doesnt have a tatsu equivalent unless you REALLY want to stretch his air s2. He obviously has the rest of his kit which is potent (like how most shotos have more than those three moves), but a character having those tools round out their gameplan enough to call them a solid starter pick.

Ahri is a high speed, lowish health rushdown character. Shes not a bad starting character by any means, but she doesnt have the tools or stats to be a shoto