That is how champions get gutted. RIP Warwick, and to anyone that used Deathfire Grasp.
Every single champion balanced by an item in the history of ever on this game has gotten royally screwed, because when Riot changes the item again, they don't go back to said champions and revert the changes.
Veigar was originally balanced around being a 100-0 burst mage. They then reworked his kit to where he wouldn't be a 100-0 burst mage anymore, which is cool and all, but they didn't take into account that DFG was core for every Veigar, so by nerfing his ratios and taking away DFG, they hurt him more than they intended.