This isn't about gameplay hence in the misc section,this is more of the scale of the changes
You really didn't do much Riot from what i can see you basically gutted his basic abilities in return for power on his passive(which is fine) and his ult
The changes weren't really big...honestly
I mean the 
changes in terms of scale were a lot bigger then 
You could find the reason by digging through to find the red post but to paraphrase it was "meant to be a small scale change and that we are going to change him because Vel'koz does not have any specific niche that causes you to pick him so we are looking to develop that" and "his game play ability usage was 'unsatisfying' (or some thing to that effect), consisting of throwing the W through minion waves in laning."
The reason he was up for the MYMU was because Riot saw no real reason to pick him over other champions that do more. They wanted to see what they could do with him to make him pick-worthy. As of a few weeks ago, he was picked because he was fun. Not because he brought a bunch of damage or anything.
Now he will get picked because TRUE DAMAGE.
The reason they didn't change much was because they asked the boards what they felt was core on all the champions they redid. Vel-koz players said all of his kit was essential and it shouldn't be touched.
So Riot actually listened to the community and just gave you a reason to pick him (True damage).
They weren't meant to be big. People were fine with him. They didn't want riot to fix what wasn't broken.
