I'd say that's a relatively fair assessment of what happened. Riot made his E super unreliable, which made his E-reliant unreliable W functionally non-existent for anything other than wave clear. Then they made his Q unreliable, because that seemed like a good idea (they also raised the cooldown juuust so its unreliability would hurt you even more.) Then, as the only remaining reliable thing in Veigar's kit, they nerfed his ultimate. Because, uh... A 1.2 AP scaling on a single target point and click ability that does literally nothing but damage is really... OP or something?
See, the philosophy around champion balance/design is that everyone should have something that makes them "unfair" (that's why they're played, it sets them apart from the others.)
Fizz has his pole.
Lee Sin has 37 abilities.
Shaco has a stealth-blink and a good first clear.
Ekko has his entire kit.
Yasuo has his entire kit.
Riven has way too many dashes.
Amumu has absurd sustained damage and amazing initiation.
Vlad has manaless sustain.
Vayne has %health maximum true damage.
Fiora has %health maximum true damage and spell immunity.
Twisted Fate has a short cooldown 2 second stun and a massive-ranged teleport.
Pantheon has his passive, a point-and-click stun (on a jungle assassin) and a massive-ranged movement ability.
The list goes on and on, and while the individual points may vary, the general gist remains the same. Veigar's unfair thing, which was his awesome stun (one offset by massive mana costs and a high cooldown, it should be noted) Riot decided to nerf it into the ground (sure, teamfights blah de blah but it's almost completely useless in lane.) Then nerf the rest of his kit just because. This was in response to losing his most core item, by the way. (I cannot think of another champion MORE reliant on a single item than Veigar was on DFG. Old!Morde and Hextech is the only thing I can think of off the top of my head.)
He's almost in a decent place now, but that's because they've actually buffed his Q's range/speed to something workable for a skillshot so he can kinda-sorta poke, but I still don't see any compelling reason to pick Veig over any other burst mage. He just doesn't bring the insane and insanely reliable burst he used to.
So they
did buff the Q's skillshotiness? I thought it felt a bit less utterly useless than it initially did. (Only a little bit, though.)
If you want an immobile high-damage mage that scales really well into late game, has a mana sustain passive, fairly good CC, a lined skillshot Q that pierces enemies and a delayed W that is REALLY nasty to get hit by, then I'm afraid he's your only choi-ohwait, Xerath does almost everything that Veigar does, but better, from further away, with no mana issues.