Actually quite a few skills in mage and ranger trees would do same or even less damage than bow, staff or dw wand attack if they have aoe or high utility. Plus crippling strike has insanely high damage modifier anyway even compared to other warfare skills. Both of these skills have AoE, CC and battering ram is a mobility skill which is also quite cheap. They don't deserve high damage modifiers. Exact numbers are debatable.
If they don't deserve damage modifiers they don't deserve increased AP costs. If two handed skills cost +1 AP like you suggested AND these skills didn't have damage modifiers I would only use basic attacks, because it would be more efficient.
Battering ram would still be 2 AP + knockdown + teleport + AoE damage. Compared to 2 AP single target auto attack I'd say it dealing bit less single target damage would be totally fine.
Crippling strike is AoE + AoE debuff, at 3 AP it would still be very beneficial to use if you can hit more than 1 target (which should be the case with most AoE skills, they should not be good for single target damage). Maybe it can have bit higher damage modifier than battering ram cause no mobility and not as good at CC.
High damage skills should be the ones that have little utility, and AoE skills should not outdamage single target ones (like it happens with crippling strike compared to many other skills).
Anyway, after some thinking, I'm inclined than the best approach would be to reduce 2h damage across the board to 1.3-1.5 1h damage and likewise nerf offhand damage to the same 30%-50%, while leaving skill AP costs as is. This would be easier from balancing standpoint.
Plus nerf rage/crippling strike/battering ram.
