In Army of the Dead, the society of Alpha zombies wasn't bitten at random, they're carefully selected by Zeus (Richard Cetrone). After his initial breakout, Zeus turned a few soldiers into Alpha zombies, but whenever those Alphas bite people, only it turns them into regular shambler zombies, so the only way for someone to become the smarter, faster, and stronger, Alpha zombies was for Zeus to choose to bite them, and he had high standards.
The Alpha zombies were almost entirely unknown, with even some of the biggest zombie fighters during the war, like Scott Ward (Dave Bautista) or Maria Cruz (Ana de la Reguera), being ignorant of their existence, with Lilly the coyote and Vanderohe (Omari Hardwick) expressing a familiarity. Their relative obscurity is a sign of how few of them there are, with only around 500 Alphas in a city full of shamblers, so it's clearly a very carefully selected crowd.
Zack Snyder explains Zeus' methods in the book Army of the Dead: A Film by Zack Snyder: The Making of the Film by Peter Aperlo: "Depending on your importance, your physicality, if you're a good candidate, then Zeus is more likely to turn you than if you were caught randomly. Zeus is doing that in a very careful way. He's not just turning anyone into an Alpha. He's very deliberate. It's like joining a club." So, while the Alpha zombies are naturally stronger and faster than most humans, they're also selected from the cream of the crop, for both physical and non-physical attributes.
Zeus isn't a typical movie monster in that his goals aren't necessarily nefarious, as he's actually trying to find a way to grow his people without having to hurt humans. The most obvious element of this effort was the creation of the Alpha zombie baby, but he was also trying to keep his selection of a higher quality. Higher quality Alpha zombies mean hopefully he doesn't have to make as many, meaning he's growing his army in the least violent way he's able to with his current resources, hoping to eliminate that need altogether once Alpha zombies are able to have babies. If Zeus is hoping other Alpha zombies will also be able to reproduce, then he's also essentially selecting breeding stock, ensuring the first generation of natural-born Alpha zombies are as strong as possible.
This also says something about Vanderohe and Scott. Zeus bit them, while he allowed other members of the team to be killed. Arguably both Lily and Deiter could have been bitten off-screen (even Vanderohe's bite wasn't seen on screen), but it's not clear if either of them survived the nuclear blast. It's not likely Zeus knew he was going to die when he bit Vanderohe, but he made an excellent choice for the next Zeus. It'll be interesting to see if Vanderohe has similar standards for his own army of Alphas once he arrives in Mexico City.