unless you also have poke, at which point why should hers be so much better?
Only very few spells in the game are less reliable than Nidalee's Q. Xerath's Q, Zigg's Q (although definitely lower range), Jayce's Q are all considerably more reliable than Nidalee's spear. Risk/reward in a big strength/low reliability way.
Also, as I hinted at: Nidalee is far less versatile than other pokey champions. Xerath, Ziggs, Jayce all have good reliable burst, comparable defensive mobility (Ziggs and Jayce at least), they have CC (even hard-CC), they have great reliable DPS. In short: They have teamfight power and higher reliability on their kit.
The argument against it is nidalee's mistakes should matter
Her mistakes do matter. First, her mana is limited she doesn't have unlimited tries to hit her spears. Second, it is very much possible to hard-engage on a Nidalee, just not with every champion. Third, the moment when Nid's mistakes matter most is if hard-engage on her team. She either lands one of her first 2-3 spears on a priority target or her team loses the fight 9/10 times. This is a very accurate statement to make, assuming somewhat even gold and skill/coordination from the teams. She has almost no power if she doesn't land spears. I'm certain if her spear was removed from her kit (without any other changes), literally every champion would be considerably better in every ELO than her at literally everything. This is just to try to help you understand how hugely she relies on her Q. If you dodge it, she is the definition of useless + a strong heal, which is only really relevant if the ADC is hyperfed and you do a bad job of kiting or nuking the ADC.
Just because she's good at poking doesn't mean the other team should just lose if forced into defending a siege.
Dodge the spears til she's oom, or hard-engage. You are not meant to WIN the poke-game vs her - as in poke her team down with a single Jayce E+Q, 2 Xerath/Ziggs Qs - you can easily survive it by playing well.
A siege is very difficult to set up, though. You need vision to prevent flanks (=hard-engage) and good minion-wave control. These two factors, vision and wave-control, will single-handedly fuck the average soloqueue team over if it is worse than the opposing team in those aspects, no matter if Nid is in the game or not.