Updated

This analyst is spoiling for a fight.

Apple’s new iPad Air and Retina iPad mini have widely been called the best tablets ever to have debuted in their respective categories. In the 10-inch range, the Air is the fastest and lightest slate yet. In the 8-inch range, the Retina iPad mini is also the best-reviewed tablet ever to have launched.

Many industry watchers expect on-year iPad sales to grow by a double-digit percentage in the current quarter and in the September quarter this year, the iPad brought in more than $6.1 billion in revenue for Apple.

But in the what the heck of the week, one analyst explains why he isn’t happy at all with Apple’s iPad line.

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UBS’s Steve Milunovich on Thursday issued a research note to clients in which he reiterated his Neutral rating on Apple shares with a $540 price target. The analyst explained that he has been disappointed with Apple’s iPad sales and that tablets in general are at risk from sales of smartphones, phablets… and PCs. The tablet simply isn’t a “must-have” device, he explained.

“The smartphone is best at keeping people in contact with friends and family. The PC’s differentiation is to do work with productivity apps. The tablet is particularly good at entertainment,” Milunovich wrote in the note, which was picked up by Barron’s. “Content creation is the tablet’s Achilles heel. So far Apple appears okay with that, but an alternative is to develop a convertible product aimed at a different job to be done.”

The answer, it would seem, is a netbook.

The analyst also noted that Apple is losing tablet market share very quickly as white box vendors gain steam, but he’s not terribly concerned about that. Rightfully so. Instead, Milunovich’s main complaint appears to be the fact that the iPad is “not on the same growth curve as the iPhone at a similar point since introduction.”

If the measure of the iPad’s success is growth versus the iPhone, we suppose the analyst is right to be worried. Then again, the tablet market as we know it today is three years old. Whereas the iPhone broke into an established market and stole business from other companies as people who already owned cell phones upgraded to the iPhone, the iPad broke new ground. Sure it’s stealing some sales from the PC market, but many who buy the iPad or any other tablet are not replacing a device from a different category.

Instead, they’re spending money that they would not have otherwise spent.

Despite his disappointment, Milunovich believes the debuts of Apple’s new iPad Air and Retina iPad mini will drive iPad sales to 25 million units during the holiday quarter, which would be mark 9 percent growth on-year. And that year-ago quarter, mind you, was the quarter in which Apple launched the original iPad mini and pulled in a wave of new buyers.

Disappointing indeed.