Actually his waveclear will be godlike with the E augment causing the total lazor dmg with explosion to do 390 dmg with a 1.1 ap ratio, and luckily minions are dumb and likely to be hit with the entire lazor dmg. He can just max E, get E augment and when it starts oneshotting the wave (which doesnt even require max rank) he can then change to maxing Q or just finishing maxing E based on what he wants to do more (better potential in teamfights or better reliable but single target dmg).
As far as picking him vs the others, orianna does far less dmg overall if Vitkor can land at least 1 ult tick besides the intitial and/or the E explosion, velkoz is an artillery mage and not a disruptor so I will not compare them as the classes sorta define their different strengths, and heimerdinger lacks damage without his turrets which easily die to any aoe abilities late game, but both do offer pretty good zone control and dps through their ults thought heimer turrets have a tendency to focus enemies down one at a time instead of hitting multiple enemies at once like viktor.
He honestly outdamages most mages if he lands his E explosion and at least one additional tick of dmg after the initial part of his ult.
I'm not necessarily defending the changes, cause even with all I have said idk if I would recommend him in soloque actually, but I did want to answer why he would be picked which the thread asks and I felt compelled to answer since I see what riot is trying to turn him into: a disruptor mage with zone control and waveclear instead of the aoe burst mage he used to be (i initially thought they wanted him to be a battle mage but he doesnt have good enough defenses and instead he changes the entire battlefield with his abilites). The fact that these changes change the type of mage he will be and thus his playstyle really sucks for those who play him currently, myself included.
I'm not a fan of the lazor delay at all personally, and I feel the ult should have faster tick rate with more smoothed out dps (honestly the dps ult instead of burst ult makes more sense to me so I like the idea of that change if not the exact execution of it).
I am just hoping to answer what he role he would play on a team and why you would pick him assuming the changes go through. Is he good enough at what he tries to do? Idk since i cant test it a lot and can only watch footage of gameplay, but I figured I would answer why you would pick him, though if it wasnt for the fact that I love him as a character and thematically, I probably wouldnt play him since he just seems too unreliable without team help. In things like LCS though, I feel they might pick him for the reasons I mentioned.
TLDR: he has very strong zone control due to the potential for honestly absurd amounts of dmg if its, and absurdly good waveclear.
Hope this helps at least give insight and hope i didnt come off mean or anything, just adding to discussion since you do bring up good follow up questions.
Eggnivia.
Using W.
Someone being Withered.
Someone stunned by Parallel Convergence.
After W
without his plane
Someone being Zhonya'd.
Using W
's human W
's turrets
's squirrels
AFK 
while rooted
move faster then Viktor new E
