Yes, if you create the perfect situation for elemental bonuses they are the best. Similarly, if you use the skill you have bonuses for then those bonuses are better.
My point is, skill bonuses limit you to skills, leaving open all rune options for them. Elemental bonuses limit you to elements, limiting you to a comparatively larger amount skills, but quite possible less runes per skill. These are very different limitations in practice and I definitely wouldn\'t call either more generic. It all depends on what you want to accomplish with your build.
Another thing I forgot to add before is that on Rares elemental bonuses may spawn in slots: amulets and bracers. On the other hand skill bonuses spawn in 6 slots: shoulder, helm, gloves, chest armor, belt, boots. There are 3 skill groups, each of which spawns in two of those slots I mentioned. So actually, you can get twice the bonus for 3 skills if you choose to boost two element and the same amount of bonus if you choose to boost only one.