Mages with a utility spell on their ultimate tend to be problematic in terms of burst (Please Read)

Most mages are extremely burst oriented, like Xerath, Brand, Viktor, or Taliyah. One problem that makes the first three seemingly easier to balance is simply the fact that a lot of their burst is limited by one major cooldown, their ultimate. That same problem does not seem to hold true for Taliyah, Azir, or even Ryze, who don't really need to wait on major cooldowns to blow somebody up. I think that therein lies the problem; if one of those three champions wants to blow somebody up, all they have to do is hit their three basic spells in the most effective order. Their ultimate does not play a major role in them getting their burst off. If they fail to do so, they only have to wait 10-20 seconds if anything to try and so again. On the contrary, if Viktor, Brand, or Xerath intend on bursting somebody down, they are gated by their ultimate cooldown, so if they fail, it will take them a while to be able to try to burst another champion down again, giving them a large window of vulnerability or inability to fight.

Low cooldown burst can be unhealthy for the game, or at least it seems as such. I really don't have any ideas about how someone would go about fixing that, but it is just a problem that I find exists in the game.