But the point is, if you are playing against relatively smart people (average) they won't randomly spread up at mid tower, they'll try to stay near eachother and try to force a teamfight. Why would they force a teamfight? Because you, as Nidalee are a poke-oriented champion, and have little to no use in an actual teamfight, if they have a malphite and he ults your carry, they go in 5v4, because you were on the side, throwing spears. You wouldn't even be in range to reduce their armor with W, or heal your carry.
Another point to take into consideration is that by the time you finish the gauntlet, the enemy carry would probably have a Bloodthirster. And what happens if you poke an enemy carry who has a Bloodthirster? 3-5 hits on the minion, oh your spear is invalid again. Even better if it was an Ezreal or Sivir, since Ezreal could easily regain hp by just poking your teammates with his Q. Or Sivir could completly ignore your spears by just spellshielding them.
If they are actually smart, they would ward where you were throwing your spears from, so they could avoid them easily. This isn't saying that every LoL player uses their brain as well as others, but it's common sense to avoid the spears you see heading towards you. So you're not going to hit every spear, you'll much rather hit 3 out of 10 spears, realistically speaking.
Also on the point of chasing enemies, what could Iceborn Gauntlet do, that a Shurelia's use couldn't? You would gain the movement speed needed to catch up with them (most importantly, your teammates would gain the speed).
In the end, it's just your opinion vs other people's opinions, just considering the fact that most people agree that AP Nidalee support isn't such a great support. In my own experience, I rarely see Nidalee supports and when I see them, they usually fail. Just my €0.02.