There is a huge gap between the two processes in terms of performance and labor cost. First of all, 7 nanometers is definitely much better than the former. Because the finer process means cramming more transistors and electrical components into the same volume, performance increases dramatically.
In terms of power consumption, 7 nm makes more full use of energy, reducing the waste of electricity. But depending on where they are used, 28nm chips still have a wide range of uses.