Beef – ground beef

I have heard that you can get the fattiest type, drain the grease as normal, and then rinse the meat with water in a colander to make it equivalent to the extra lean fat content. I'm not sure I buy that, and it seems this would rinse off any seasonings used also.

That sounds terrible. Cooked ground beef should be drained if necessary, but not rinsed. It will rinse away a lot of flavor, and I doubt it makes it the equivalent of having bought lean meat in the first place. There is still plenty of fat present in the meat itself.

If you want low fat get extra lean. If you want flavor get 80/20 or 70/30 and drain thoroughly for as little fat as possible. Do yourself a favor though and don't rinse it with water.

To get more flavor out of cumin, you can use whole seeds, and toast them briefly in a pan before grinding. If you don't want to put forth that extra effort, you'll just need to add more cumin. If it's not salty enough, the best solution is to just add more salt (sorry). Salt will enhance the other flavors as well. A bit of cornstarch would help make the spices stick, and dry out the mixture. I'm not sure how much water and vinegar you're adding, but you may just be watering down your beef too much. I usually add just enough to keep the spices from sticking to the pan, but not so much that there is a lot of extra liquid that needs to be reduced.

Your spice mixtures may also contain some form of MSG. You can get a similar umami "punch" by adding a dash of Worcestershire sauce.

Edit: I don't know how I missed this, but the other answers point out the lack of garlic and onion. Your store-bought spice mixtures definitely contain plenty of those in powdered form, which you can use, but fresh is tasty too. Don't add fresh garlic too early, as it can easily burn and turn bitter.