There are horses abandoned by man in an African desert.

[Catherine]

I know that the horses that live wild in North America are fine. They fit right in and are adapted to life here. There actually were prehistoric horses that went extinct so the modern feral horses may be helping to restore the balance of nature.

The Namibian horses are different or perhaps not. They have been living there long enough to have adapted to the environment. What has changed is  the conditions. There was a severe period  of drought. It did cost the lives of most of the foals. It pushed their main predator the hyenas to desperation. They killed many more horses because they were in need. The drought is over and the horses are making a comeback.  They might require some help to survive, but they can survive.

https://www.cnn.com/travel/article/namib...index.html

https://www.wild-horses-namibia.com/


I am not agreeing with your view of the situation. The horses are adapted to their environment. They have survived for over a century so they must have some degree of stability. They do require help right now because of a severe drought. It is easy to judge their lives as miserable because we would consider the conditions  miserable. The horses are living free and wild and they seem happy with that. Horses seem to be able to adapt and return to the wild. Not all species can do that, but horses definitely can. They do seem to favour dry grassy plains. 
The true wild horse, the Przewalski's horse, lives in Mongolia in the Gobi Desert.  Namibia might be a bit drier and hotter, but the conditions are not that different.  When the conditions are good, Namibia is able to sustain the horses. If the conditions remain good for a few years, the horse could make a comeback.
They will need our help though.