As long as you get the right amount of calories and nutrients, keto can be healthy long-term, as can veganism. People should chose the diet that works for them. The diet they like enough to follow.

For me, keto naturally reduces calories. I'm not the kind of person to overeat bacon or butter. I like them, but I won't overeat them. Whereas when I was vegan I found myself overeating a variety of things.