Hey, I'm the guy that gave you those Nasus tips a few days ago. Let me see if I can help you out here.
First of all, you have to remember that gangplank did about 750-800 dmg to you. That's a 1/3 of your health bar, so Veigar had a much easier time doing what he had to do since you had less health. Due to his void staff, and the fact you do not have much health, if he hits his Q and his W on you, then yes he will kill you with his ult.
Now, Veigar really isn't op. He can be very annoying to face late game yes, and when fed it can be very hard to deal with him if you and your team are not on the same page. But his winrate is at an avg 50.5% currently. He has some severe weaknesses that you can exploit, as long as it isn't like 4 hours into the game.
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He is immobile, no sustain, AND squishy. If you get on top of him, he just kinda melts.
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He is heavily skill-shot reliant. Ever since his change that made his E and Q harder to land, he's been given a lot more counterplay. It is very hard to hit his W without his E, or good predictions. His Q, altho easier to hit, can still be predicted and avoided. If you manage to not get stunned in his E and properly dodge while inside the cage, you can basically avoid all his damage.
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His early game is quite meh, and has a very bad winrate at 20-25 minutes. I know you're playing Nasus, but that means you can exploit that time if you're ahead.
I will admit that Veigar has been slowly rising up every few patches, but reason is because after he rises up slightly, he goes down again a patch or two later. Maybe this will be his big break, but we'll have to see. Currently however, he does not need a nerf.
I don't know why you built Frozen Heart AND trinity force tho, that build is kind of outdated. I myself am still a fan of trinity force, but I have stopped building Frozen Heart on Nasus over a year ago. It just isn't a good item on him after item changes and FH's nerf.
Try Zz'rot Portal over that and Frozen Heart if you want to keep trinity force, ofc make sure to rush CDR when possible. Or, you can rush Iceborn Gauntlet if you want to be more tankier for slightly less damage and mobility.
Also: You have like no health. Of course Veigar is going to 1-shot you if you're all MR but no health and he has a void staff. Make sure to buy health items as well. Also, is Veigar fed? He just might be doing that much since hes fed.
TL;DR: Veigar is currently actually balanced or very near it right now, GP did 1/3 of ur Hp Bar which set up Veigar, and your build is not the most optimal.