Was the width of current Vel'Koz's ult deemed to thick and one of the goals of the VFX to change that? I've never seen any complaints about it previously and I would think "big area effect damage that hurts a lot and slows" is as good a reason as any to have a lot of visual noise for. And especially since the ability is THE HIGH POINT of this champion it should have a big visual effect.
There's a difference between having something noisy and important-looking on a large area, and having something completely obscure said area, especially over such a long duration.