Phragmites australis americanus (American Common Reed) and Phragmites australis australis (European Common Reed) are not only similar species; they are the same species. But Phragmites australis australis is one of the most damaging invasives in North American wetlands. Genetic relatedness to a native species is a poor metric for decerning if the potentially invasive organism fulfills the same ecological role.
I agree the addition of predators would likely change the dynamics of feral horses in the U.S., and I’m saying all of this, not to be combative, but rather to weigh in on what in my opinion is a common misconception regarding ice age horses and feral horses. The success of many invasives can be attributed in part to being moved to areas where they have no predators/natural controls.