Good thread.
I always make my own rubs and I never add salt to them. I much prefer to salt the meat first, where I can control coverage/evenness, and apply rub over that. I let the salted meat sit while I make the rub, allowing the salt to draw a bit of moisture to the surface. That helps the rub stick and, imo, helps in bark formation. It also allows me to apply as little or as much rub as I want without worrying about whether there will be too little or too much salt at the finish.
I agree that simple is often better, but simple--to me--does not necessarily mean few ingredients. It can, but doesn't have to. Some of my rubs have quite a few ingredients (some items complement others; some offer contrast), but the overall flavor profile--when blended and cooked-- is simple. I totally agree that rubs should not overwhelm the meat, no matter what their composition. But much of that has to do with the meat, cooking method, and amount of rub used. I make an Moroccan-style rub called raz-el-hanout that, in itself, is very complex (there are near 60 herbs/spices in the mix), but I don't load up the game hens with it; it does not overwhelm the meat at serving.
I do not buy commercial rubs though I have no issue with those who choose to. Not everyone is into that part of the Q or cooking process which is perfectly fine. I'm often asked about rubs, however, by people who are either looking for new ideas/profiles for their rubs or looking for simple tweaks to rubs they already make. One of the first things I tell them: Ditch the paprika. First, unless you're buying very high quality paprika it does not add a whole lot to the rub in flavor terms. Even the best quality stuff that I get--while flavorful (as it goes)--adds less than it 'should' considering the volume seen in many rub mixes.
But: Paprika is a good carrier (it blends with, then 'carries', the other ingredients in the rub) and adds volume. It is cheap (even high-end is not expensive; the low-end is very cheap), which is why it is in so many commercial preparations. I use it as a carrier in a few rubs. Mostly, though, I use a blend of pure ground chilies for most Q rubs. In this way I can ditch the cayenne(has heat but virtually no flavor) as well. Pure ground chilies have varying flavors (fruity, earthy, bright, deep, lemony, et. al.) and varying heat levels and intensities (from none to extremely hot; from very forward tip-of-tongue heat to sneak-from-behind to subtle post-swallow heat). I find that blending pure chile powders works to kill several proverbial birds with one stone: I can use more of a mild or 'warm' fruity Ancho, say, which adds flavors and the bulk of the carrying, and blend it with one, two, or more of other chilies thereby adding more and different flavor and heat components as well as other qualities. This adds to the overall complexity of the rub recipe--perhaps--but does not result in an overwhelming finish when applied and cooked. Quite the contrary I think.
Anyway, something to consider.