The reason they look different is that they have to be formulated differently for thier method of application. Even if you use a bottled paint, the airbrushed result will look at least slightly different from the hand-brushed result, simply because the method of application was different. The situation varies with the degree of gloss, too. Sometimes, gloss paints are easier to touch up than flats—but that varies.
There are two techniques that can be used to blend in areas that have been touched up with a brush, provided that the paint systems are the same (acrylic on acrylic, enamel on enamel). One is to apply the brushed paint either in a thinned state, or apply thinner to the tack free surface. This works best with gloss paints.
The other is to polish the painted surface with very fine grit sandpaper (>1000 grit). Then coat with a clear gloss, followed by a clear flat if the final finish is to be flat.
And yes you are ready for an airbrush! Rattle cans are inefficient, wasteful, expensive, and "environmentally unfriendly." The only reason to use them on a model is a slight increase in speed—at the expense of everything else. A good airbrush is not very expensive, even including the compressor and tank. (My entire rig cost me $100, about half for a T&C Omni 4000, the rest for the compressor. It pays to shop around!) How many rattle cans is that? How long will the rattle cans last? It is entirely possible that a grandchild will be using my rig when I've been compost for fifty years.