alright, do a direct comparison between veigar at 5.3 and current veigar.
observe the wall of text and layers of complexity they added. now observe the wildly lower cooldowns, mana costs, and higher damages which is compounded by 3x farming rate of what he used to have. (ap on assists did not exist)
veigar was at least simple and easy to use back then, very hit/miss and it was a niche role to fill, you either had the skill to land the stun or you found yourself dead.... to everything.
the most hampering thing was his stun range of a mere auto attacks range away. or 850 if you added to the diameter of the ring into the equation. leaving himself exposed to literally every other cc ability imaginable making veigar be aggressive or the one to initiate the fight. or to tag onto a team mates cc and secure the kills.
the whole reason veigar saw "dfg compensation" to begin with was to shut down his E as a support ability to stop hyper mobile champions (kalista) who were just added and prime in the LCS.
reminder, deathfire grasp was removed at the end of season 4. veigar went a whole half a season with a decent win rate of 47~48% in that time frame making the champion work anyway despite not having his prime damage ramp item. players found other ways to make him work. he didn't "need" the compensation back then, it was forced onto him with the intention of removing his stun off the planet, which they did.