I think that blizz figured out wrongly that for AoE to be strong vs. Protoss it needs to have this + vs. shields damage. Protoss is inherently more sturdy vs. AoE since it uses quality over quantity units, however this is also being exacerbated by the lazy approach of not having inner and outer radius damage on the AoEs. I'm talking about the flat damage AoE that baneling, Widow Mine, Disruptor, Liberator uses. Imagine if siege tanks dealt 40+30 dmg in its entire AoE, on +2 it would one shot all the marines in its entire AoE rendering the unit obsolete. Now imagine if did its outer ring's dmg to all of the units in the AoE, now Stalkers would mob the floor with siege tanks, it wouldn't even be funny. It becomes very binary how well the unit will do and that is often stated as the reason why the disruptor is frustrating.
I think there is a place for this approach, I wouldn't want to introduce different AoE radi to the baneling, it's meant to be binary, you kill the lings, marines, or you don't. I shall just mention the +2 killing of workers, another approach instead of meddling with how upgrades work, they could've just reduced the AoE from its incredible 2.2 AoE down to 2 and it would've delivered the same effect of reducing this worker killing power without taking a cool interaction away, or at least reducing it to lvl 3, where zerg alrdy gain most of its power. Another thing about the baneling is the spell dmg vs. structures, it shouldn't really benefit from upgrades, because if it's smth that can be improved/fortified against, then armour values should help against this attack. Just look at how the oracle beam was handled for the duration of a patch, it was to become affected by both upgrades and armour. I'm thinking they kept the baneling this way(spell damage) so that it's easy to count the number of banes needed to blow up a depot, but then it should not benefit from upgrades.
The three other units could be handled as follows:
Disruptor deals 100 +100 vs. armoured in 0.1 radius, basically if the unit sits on top of another unit within its collision, it will do this much damage. This also means that it cannot hit structures, or siege tanks, because it cannot get on top of those units. Then it has 60+60 vs. armoured in 1.5 radius, the radius it has now, meaning it blows up Marauders that stim, but doesn't kill afk marauders because of the 125 hp. It will perform way worse vs. non-armoured units, but then it also has a 1.75 radius of 30+30 vs. armoured. Admittedly this does destroy banes quite a bit, but then I'm not sure why the bane needs to be a 30, and not 35 hp unit. But as it stands now it would be a great counter to Banes, and armoured units, especially massed armoured units which uniquely is a big thing in sc2, Marauders, stalkers and roaches. This makes Disruptor different from storm which has flat dmg, and colossus which has flat dmg and + vs. light.
It can still one shot disruptors and will be able to one shot unsieged tanks, and lurkers but only within closer and more exposed ranges and it will probably mostly hit one unit, but it will be able to hit two targets.
The Widow Mine, I always wanted to be redesigned to be anti mechanical, an anti tank mine, but giving it some strong AoE is perfectly as viable. 160 dmg on the sentinel missile, 60 dmg splash in 1.25r, 30 dmg in 1.5r(current AoE, after nerf), 15 dmg in 1.75r. In general this would be an ever so slightly stronger unit, especially its interaction with Marines and Banes, probably weaker vs. lings. Oh, and only the inner most radius would one shot probes, drones and scvs, that is probably how it should've always been.
The Liberator AoE is the lamest attack in SC2, it took me 7 years to adjust to seeing how slowly they kill overlords, from the number one terrible, terrible damage race. I don't know the intricacies of the Valkyrie in bw, but I still imagine my AoE change to this unit, would bring it closer to that unit.
The Liberator:
6+2 vs. armoured in 0.7r, 50% dmg in 1.4r, and 25% dmg in 1.5r.
I played around with this version and it just feels more like a normal unit. I think it's great.
There are other AoE gripes of mine, but let's keep it at that, what do you think?, if you think I screwed over the baneling, I kind of did, I prefer to have a 35hp baneling with dmg and upgrades how they were in WoL/HotS, but with only 2r AoE. One reason why I like this, is because it rewards splitting the marines, instead of focus firing and picking up, but that's another discussion.
Thoughts?