And further, abilities are added usually during expansions and stuff, ie dungeons, raids, etc, are tuned around those abilities.

So I'm not sure how you could "merge" ib and fc for instance without throwing off that balance and tuning. If fc and ib and steel cyclone and decimate were "merged", would warriors get replacement abilities for lvl 50 to 60?

You can't cuz that stuff is done, and you ought to not mess with it. Would you give new abilities to wars lvl 60 to 70?

Well "merging" these abilities is not needed is it? SE could add new abilities now if they wanted.