Totally doable, but when you can fab up an 2' tall aluminum letter in 15 minutes, $10 in materials, vs 150 minutes, sectioned out, $5 in materials, you just can't compete. (Obviously you have a great upfront investment in machines for aluminum, less so for printing) It'll get there one day, and is in fact viable at tiny sizes. A 2" letter is going to take a lot more care to fab out of aluminum, may show imperfections, and is challenging to paint. 3d printed could be printed with whatever color, is pretty well set and forget, and it'll mostly get all the details easily. Plus you have to consider life of the plastic. PLA is organic and breaks down pretty rapidly without a coating, which brings us to the paint booth, where with aluminum you could order precoated stock.
The best letter I did was printed onto 1/8" acrylic, then cut out with a router with a flush trim bit. It worked great, but it had .25" inside radi, was still subject to human shortcomings, and I had to preheat and clamp the acrylic to get it flat enough to take the filament with enough of a bond to not just fall apart.