Necromorphs are just zombies with a hive-mind. Xenomorphs also have a hive-mind, and are a lot more dangerous. Necromorphs are loud, clumsy and predictable. Xenomorphs are silent, agile, powerful, heavily armoured, can walk on walls, and can learn from their mistakes. I read a novel series based on the Xenomorphs, and the first novel ended with them taking over Earth. The first nests were enormous, and easily found like on their homeworld. The xenomorphs learned after the first nests were destroyed, and started making many small nests, with only a few eggs in each one. Some of the xenomorph colonies were using wildlife instead of humans as hosts.
Another benefit to the xenomorph's breeding method is that you can't tell if someone is a host just by looking at them, so the xenomorphs could set people free after impregnating them. If someone is carrying a queen, they could wander around for days before it's born. With the necromorphs, it's obvious who is a threat, and who is not.