What exactly do you mean by a "failed" mod? There seem to be a couple definitions in use in these RNG discussions:
1: The mod caused the equipment to be objectively worse, i.e.: the red (negative) stat changes massively outweighed the blue (positive) stat changes. Note that a mod can be useful if you're trading one type of stat for another, e.g.: greater FSD range for higher power draw, as long as the relative trade is balanced (although a trade in your favour is even better, obviously). So I wouldn't classify that as a "fail" of this type.
2: You had certain expectations, and the mod isn't meeting those expectations. e.g.: FSD range increase of at least 2LY with no greater than 0.5 power draw increase.
So the "type 1" fails I can sympathise with, but it's also my understanding that FD have taken steps to dramatically reduce the probability of getting these types of fail. You certainly shouldn't be getting them several times in a row. If that's really the case, then yes, I think FD should tweak it some more.
The "type 2" fails… These just seem to be an indirect way for people to say that they want to be able to min/max their builds to reach (or very nearly reach) some pre-determined "optimum" module spec (i.e.: achieve the current meta-of-the-day), and that the Engineer "failures" prevent them from doing that. Personally I don't have much sympathy with this line of thinking. It seems that the whole point of Engineers is to make your ship better in a quirky, individual way, rather than allow for a particular target spec to be achieved. And personally, I love that idea. YMMV obviously, but for that reason I'm a "No" voter.