If I need to block in a lot of color at once while I'm painting with acrylics, I usually end up doing at least 2-3 layers, even if it involves applying the same color over and over. So the need to layer acrylics to get the best coverage is completely normal. The benefits of applying multiple layers are that you can achieve smooth, even coverage.

Usually my first layer will be thin, like an underpainting. Then I'll apply another thin-to-medium layer over top of that, and if necessary, another thin-to-medium layer on top of it all again. It's a multi-step process, but since acrylics dry so quickly, it doesn't really take that long.

Although it depends on your personal preference and the style you are working in, I would generally recommend painting in thin-to-medium layers rather than one thick layer if you are trying to cover a large area - basically for the reason that you state: when you paint in one thick layer, sometimes the coverage gets a bit uneven and you can get areas of shine here and there.

If you use black acrylic paint straight from the tube, (that is, without mixing it with any other colors or acrylic mediums), then sometimes you can indeed get that patchy shininess. Instead of using straight black, I usually mix my black with a small amount of another color, such as Prussian Blue, Raw Umber, or Dioxazine Purple. The result is still a color that is black, but it is less "loaded" with black pigment, thus appearing more normal when it is dried. I also find that mixing black with another color gives the black more of a depth and richness. If patches of shine are still a persistent problem and you would prefer more of a matte finish, you could also try mixing your black paint with Matte Medium (this links to Blick Art Materials, and if you make a purchase it helps support this site).