This seems a weird question. The Macbook being slower than your air doesn't mean that it won't be just as performant in 4 years, but no it won't be faster than a device that it isn't faster than now.
If the Macbook is fast enough for someone now, and their workload doesn't change, then yes, I'd expect it to be just fine for them in 4 years; just as the same can be said for the Air, or the others.
If the Macbook is fast enough for someone now, and their workload doesn't change, then yes, I'd expect it to be just fine for them in 4 years; just as the same can be said for the Air, or the others.