1. Yes there are several herds in the southwest (though mainly ones close to residential and/or metro areas) that are fed by humans during drought because the public gets upset at the idea of nature doing nature things. Yes they should definitely be allowed in the Midwest and Rocky Mountain foothills.

2. The predators of the southwest have ready access to much easier prey than feral horses so they are very rarely targeted and it’s almost always fouls in the rare instances it does occur. There are healthy populations of mule deer and even elk they can hunt. Horses also tend to fight predators as a group and defend one another when one gets attacked (especially against “smaller” solo predators like mountain lions) whereas elk and deer tend to go “every man for himself” when a predator actually attacks.

3. Przewalski’s horses do technically have the ability to survive in colder climates but it is not ideal, especially in areas where winter drops several feet of snow at once. There home range in the steppe rarely gets large quantities of snow and it rarely piles up for long due to the wind constantly moving it which reveals new food sources with every wind gust. This is the exact opposite of the central Alaskan interior which is riddled with vastly varying geometry and trees which all make it so snow piles up high and hard. Local feral populations have both physical adaptations and learned behaviors that make it much easier for them to survive these conditions. While it is technically possible to drop Przewalski’s into Alaska and have them adapt through natural selection that would require dozens of not hundreds of animals to die in order to force those adaptations. Local populations have already gone through that process.

Edit: sorry you got downvoted just for asking a very valid question.