Yes but how far away are you exactly from your target during a team fight? The answer is not that far at all, my only beef is with how fast it travels at long range if they would nerf that it would not affect his damage output in teamfights by much, just add like 0,5 sec on max range. At a standard range (which is you sitting in the back behind the beefy champs) during a team fight you would get a travel time increase so low it wouldn't even be noticeable. He's too good at just walking away a bit and bombing a side lane greatly helping that lane while getting back in lane in no time at all.
Come on, man. You're on the other side of the ult. When I ult I always feel the travel time is far too long because I'm the one wanting to see it land, I'm the one seeing people escaping it. It's about perspective, but if you take a step back you'll see that simply a long range ult that hits most of the time is in itself not unbalanced in anyway. You're not saying anything about numbers or his kit in general, you're making the claim that it's unbalanced just because you can't walk from the ult center to the edge in the travel time.
Why? In which relation are you making this claim? Your way of arguing is absurd.
Really only Karthus and maybe GP can do that more easily, ez's and ashe's can be dodged easily while lux's has a far shorter range. Karthus pays for having his ult with a high CD, high mana cost, long cast time and meh AP ratio (and it's his only long range damaging skills) while GP's is random damage most of which is easily avoidable and usually you just use it for the slow anyway. Ziggs needs a laughable 100 mana to cast his ult, the cooldown is pretty decent, the area of effect ridiculously large. The only drawback is that you do 25% less damage if you do not hit with the center oh and maybe it won't come off CD when you need it in lane. Not hitting anyone at all is hard due to it's radius. If karthus fails an ult it really hampers his laning because you need that mana and if the enemy gets out of defile range you can't really do crap. Ziggs does not share that problem IMO.
You can't just take a couple of champion's ults and compare, you gotta take into consideration the champion as a whole. Even IF I accepted your way arguing Karthus' ult is a sure-fire hit on all champs, so of course it needs bigger cost and bigger CD. Not that I think you can compare a bruiser like GP with a mid-laner like Ziggs at all, but even if you could, GP's range is the entire map, the area of effect is larger, and the ult has CC.
You are arguing from an extremely narrow perspective. The point is not "is the travel time too long/too short" but "how is the champion all in all - and if there's a problem with parts of his kit, what practical implications do they have and why are they a problem?"
In short, I disagree strongly with you, and would like to add an annoying "this is why we can't have nice things." They did something different with Ziggs, and already people are comparing him to a bunch of other champs saying "they don't have this, he must be overpowered". In my mind, his laning is the most powerful (because of the way Q works and the long range, he doesn't even have to push his lane to zone such as you claim, he can throw the bomb at range avoiding creep hitting, run around creep, auto-attack with passive, and get away with W). If anything needs a nerf, it's that... But the intensity with which his mana drains makes up for it I think.
Like I said, at this point my initial thoughts are "I'd take Brand or Cass over this any day."