Disrupts are an issue that is well known if you play any of the 7/24 classes that focus on doing magical dmg in the game.
Obviously some sort of help in gaining strikethrough would help, but the way OP suggests with positional checks would benefit some classes way more than others.
Sorc AoE is frontal cone, IW being the best example, followed by IS, both shot forwards from Sorc in a cone. SP is also somewhat in same category, same with DC, they launch from Sorc outwards in all directions. Only SK and PoS are anchored in some distant target/area and dmg spreads from there.
BW meanwhile has same SP=SE and DC=Anni as Sorc, but instead of IW there is previously instacast, now 1.5sec Fieryblast that is launched at target, and from there explodes to other nearby targets, Detonate being kinda similar. Flamebreath/IS are kinda similar, same with FBB(much shorter CD, much faster hits, awesome synergy with FF)/SK.
BW with fast Fieryblasts and easier usable FBB would gain far better advantage than Sorc that far more relies on frontal cone AoE dmg. (example, target 1.5s Fieryblast at a Choppa standing behind 8 tanks or on a heavy armoured low willpower DoK - whereas Sorc IW just hits the tank wall in the front.)
What I'd rather see is change the way Willpower gives Disrupt, say instead of current ratio it would be 75% of the previous or 50% and see how it would require further tuning.
Or something that I've thought of before, have Willpower and Initiative count together into a common pool, with the end sum being divided by 2, which then gives that amount of Dodge, Disrupt and chance-to-be-crit. (effectively giving healers less disrupt, but far lower chance to be crit, and possibly better dodge ratios) [and OTOH, classes with low Willpower would have their Init value giving better Disrupt chance, while now needing even more Init to get lower chance to be crit - which might however require further tuning with the Chance-to-be-crit formula to avoid extremes on either end of the scale.]
Or another idea; remove Init from feeding to defence check values, and have 50% of Willpower rate feed into Disrupts, and the other 50% into Dodge. Init would focus solely on C-t-b-Crit, and if you want good decent defences against A L L RDPS, focus solely on high willpower, healers gain less Disrupt but better Dodge rate, less annoying for magical dps but surely more annoying for physical rdps. Would be certainly more evened out state of balance with "Dodge-Disrupt-Dodge-Disrupt" than "Disrupt-Disrupt-Disrupt-Disrupt".