Preferably sooner rather than later.
After decaying from Diamond to Gold, I played Vel'koz from Gold I back to Platinum II with 64% win rate. Now as I approach Diamond V, my win rate with Vel has dropped to 54%, because he and every other AP carry that doesn't have Annie or Syndra-style burst is just not viable when every game is full of assassins and mechanically skilled AD carries.
ChallengerTier1 votesStep 1. Roam bot. Step 2. Kill enemy bot lane. Step 3. Your support gets ardent censer. Step 4. Win the game.
Khristophoros1 votesIt's not because he lacks instant burst. He can kill from a safe distance and his full combo deals more damage than most other champions if you land all of it. In many situations there's actually no counterplay, but that is assuming you already landed stuff and all the positioning is correct, so the time for your target to have counterplay has passed. So once you achieve that scenario, the slowness of his combo damage is not a problem.
The problem that I run into with Vel'Koz is the better my opponents are the harder it is to land abilities. So much of his damage is gated behind landing his skillshots. It's probably necessary to balance his safe range and how much CC he actually has at that range, but it poses an issue against good players. Lower elo players are easy to hit with his skillshots and you just evaporate them. On the flip side, high elo players are harder to hit and they position better.
I don't think it's a problem that warrants changes because I think the potential is there to become more consistent at outplaying people with his kit. Of course, champions with cheesy "guaranteed" mechanics will always be more popular but it doesn't actually matter. It doesn't mean Vel'koz doesn't have higher potential than those champions. Personally I think he does.
And if you disagree I have to seriously ask why you main him.
Yenn1 votesIt's not because he lacks instant burst. He can kill from a safe distance and his full combo deals more damage than most other champions if you land all of it. In many situations there's actually no counterplay, but that is assuming you already landed stuff and all the positioning is correct, so the time for your target to have counterplay has passed. So once you achieve that scenario, the slowness of his combo damage is not a problem. The problem that I run into with Vel'Koz is the better my opponents are the harder it is to land abilities. So much of his damage is gated behind landing his skillshots. It's probably necessary to balance his safe range and how much CC he actually has at that range, but it poses an issue against good players. Lower elo players are easy to hit with his skillshots and you just evaporate them. On the flip side, high elo players are harder to hit and they position better. I don't think it's a problem that warrants changes because I think the potential is there to become more consistent at outplaying people with his kit. Of course, champions with cheesy "guaranteed" mechanics will always be more popular but it doesn't actually matter. It doesn't mean Vel'koz doesn't have higher potential than those champions. Personally I think he does.
And if you disagree I have to seriously ask why you main him.
I played him because he can stomp bad players. Around Diamond V, he's no longer viable for the reasons you stated and more, and the same applies to virtually all similar casters. Mid lane is dominated by assassins and (faster) burst casters in 9/10 games. I used Vel'koz as an example, but he's a particularly bad example because he only works against bad players and has no way to function against good players who can avoid skill shots (or mediocre players who rush movement speed).
The general problem is that you need to be able to 100 to 0 carries in a window where they can't lifesteal in order to be viable. I can drop my entire combo on a late game Draven, but he's not going to die, and then I have nothing as he runs into me with superior movement speed and three shots me.
Also, I'm not sure if we're playing the same game. His E is not a 'safe distance' against most mids, and you mean his full combo including ult, which leaves him stationary and can't turn fast enough to follow a dash at close range. There are only a few truly immobile champions who can neither retaliate from E distance or avoid it, and none of them are viable picks in general (i.e. Viktor). Though even in the case of something like Viktor.
I think the problem is that you're not playing with good players; instead, you're likely playing against players who panic and run away or react too slowly to counter your combo. i.e. no matter what I'm against, if I combo something mid lane post-6 and their Flash is up, they're going to Flash directly into me and run around me at close range to take advantage of my ult's turn speed. Bad players will just Flash away.