Illustration: Sarah Grillo/AxiosApple stock is down 15% this year, even as other Big Tech firms like Nvidia rally to new all-time highs.Worries about Apple's ability to compete on artificial intelligence, to weather tariff policy, and to outgrow competitors are piling up.Why it matters: Wall Street consensus is that the company is behind on artificial intelligence and running short on time to do something about it.What they're saying: Apple "needs the AI story because that's what's being rewarde...