I believe that AP burst isn't working fully to its potential at the moment.
Correct me if I am wrong, but with the few exceptions (Lux and Elise primarily), AP burst champions who rely on abilities to kill their targets seem to be underperforming due to the AD/Tank centered META we currently are in. There are plenty of options for AD/Tanks to survive an AP mage burst in terms of itemization and masteries (warlords bloodlust will save any ADC who happens to not be killed in the combo). Hopefully, in the future mage update, either some new items or masteries maybe, will become available for AP burst mages in terms of defensive or magic pen, so they can more easily fulfill their unique role, either by dealing more damage, or having a greater chance at surviving the brief period when their combo is on cooldown. Maybe even an item similar to how ROA scales over time.
Deathfire Grasp
that are routinely built on AD champions that work too well in shutting down AP burst mages. Like if you're an AP burst mage going against Zed, they'll rush a hexdrinker making it unfairly difficult to 1v1 unless they make a big mistake or you get a gank. Hell they'll even build all three 
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