I feel like you are making several huge mistakes.
Like, Graves was barely played and didn't do to well until a few patches ago.
He became popular and strong again due to the new jungle changes.
These changes forced the junglers to interact with each other (something a lot of them seem to heavily hate) more often than not.
And this is what propelled graves back up.
He is by no means a strong late game character. And his mid game is average.
But his clear is very healthy, and quick. Which gives him an advantage in the early game.
An advantage which he can press and use it to interact with the enemy jungler or simply do scuttle crab and get ahead in exp.
Essentially, starting to snowball. And then he can invade or gank laners.
While you people might hate hasishin
https://www.youtube.com/watch?v=smtagi5PqGg
that's a video about him talking with 2 of the people that got the high tier in na as junglers.
And you can see them being very, lets say, unhappy, about the fact that jungle isn't as impactfull in terms of shutting down the enemy jungler.
As for example a laner can shut down his enemy laner.
Mainly because of this "lack of interaction", albeit, it was a different reason for it back then.
What riot did now, is that they forced said interaction to happen, as a result, ofc, the new champions that are going to be "top tier" are those which can take advantage of the enemy jungler as well as the enemy team to some degree.
ps, if you watch the video, you'll hear a lot of crying about tanks, try not to get to caught up in that.
So, the point of this post is to say that graves is not a:
ranged drain tank assassin adc that can jungle at 100% hp the entire clear and is strong early mid and late game.
He is not stronger than a tank late game.
He is not stronger than a traditional adc late game.
He is not stronger than a mage late game.
He is most likely around a bruiser's level. Good early and mid, falls off later.
Because of this, he isn't really an "adc". He won't be building crit or on-hit damage items, he will be building a hybrid of sorts.
http://na.op.gg/champion/graves/statistics/jungle
You can see black cleaver in there, you can see yommus in there, and you can see warriors and phantom dancer and most build items.
Looking on his items statistics, we can see that Life steal items, required to be a 'drain tank' unless you got life steal in your kit (like 
or 
) have only like 1.6% pick rate for Death's Dance and 1.5% for Maw and 1.2% for vampiric scepter.
Which means, in about 95.7% of the games, Graves doesn't have life steal.
Hence, not a drain tank.
Even Duskblade only has a 3.6% pick ratio, meaning, he won't be picking the "Assassin" item either in most games.
Expect about 70%+ of your graves game to have something like Black Cleaver, Yomus, PD, Warrior and boots.
Which makes graves into not:
ranged drain tank assassin adc that can jungle at 100% hp the entire clear and is strong early mid and late game.
But:
short range bruiser with a very healthy clear, good mobility and is strong in the early and mid game
Which means, he relies on being able to stay ahead of the course of the game, and punishing the enemy's mistakes. Be it the laners's or jungler's.
And he has the tools to do just that.
And he is still a much more healthy pick than 
jungle...........
W 5 dmg
which most definitely heals you. So saying he doesn't build lifesteal is something of a crock.
????
