to begin, concealment is a single target dps, and it wouldn't really feel right for it to have the additional targets taking damage, in my own opinion. Lightning uses their affliction (the dot I'm assuming you mean, if I'm wrong, I apologize in advance) to get automatic crits, as well as is able to refresh it with two moves. this dot has boons already in hand. looking from a parsing perspective, in concealment poison damage from dart (i believe i am reading this right, again where I make mistakes correct me) it deals approximately 11-12% of total damage ( http://parsely.io/parser/view/50404/1 ) then in lightening the affliction takes up like 11% of the total damage ( http://parsely.io/parser/view/40603/1 ) . now lets look at engineering both electrified railgun and poisoned take up around 6-7% of total dps individually( http://parsely.io/parser/view/46240/2 ).
what does this show? I mean look at them, they are all against dummies. but when you look into bosses in hm, Interestingly enough i found an even greater disparity between the other two compared to the engineering.
(all were against ul as sadly parsley has no charts of engi going beyond that currently in hm (imo that is sad as the commanders is such an aoe fight))
so lets look at these parses.
first in concealment - poisoned(corrosive dart)/poisoned(tech) together deals about 14.5%(7.2 and 5.5) of the dps here (a relatively big chunk trust me, you'll see)
http://parsely.io/parser/view/44586/8
second in lightening - affliction makes up about 7% of total damage in that fight.
http://parsely.io/parser/view/3928/16
third in engineering - electrified deals a total of 2.2 and dart like 2%(see how small they are in this fight?)
http://parsely.io/parser/view/21038/18
So if I have properly gotten my point across, engineering, the aoe dot spec, known and made for aoe plus dots, has the two dots not taking up very much total dps. What I am trying to say is that it would be nice if one of these abilities (preferably railgun as virulence already has spreading of poisoned darts also as it looks cooler imo) would/could spread, allowing for them to be more useful in the whole aoe thing. also making engineering better at aoe.
but also not going to lie, concealment's entire lack of any aoe(that is actually helpful/not finicky) sucks and a way to increase that would be nice, but i am pretty sure they do not want to deal with their single target having less damage.
I mean, does this make any sense? or am I just crazy?? Ive played engi since launch and love it, and this question about there not being dot spreading has crossed my mind many times.