"The bull case, which I also understand, is that you take the market caps of Wal-Mart, Netflix, Salesforce, roll them all together—boom, that's what you're going to get," he said.
"The bear case is that, hey, this is a commodity retailer, and a commodity-retail play margin is about 5 percent," Gillis said. "If you look at their shipping losses, that's essentially the margin that they should be making. And there will be that period where they're going to have to grow into this valuation, from a profitability angle, over ... many years."
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Gillis had a $280-per-share price target on Amazon. The stock closed at $332.21.
"It's so difficult to trade this because it has yet to crack," he added. "People who want to play this to the downside, it's just that's never been a great move to it. You can put the sell on it because of valuation, but the stock hasn't been moving that way. But it hasn't moved that way, and it continues to ratchet up. Everyone keeps waiting for when is that quarter going to happen, when it falls out of favor, but it's not this quarter."
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Gillis also said that Wall Street analysts' guidance for the next quarter might be overly optimistic.
"Here they're guiding from a loss of $500 million operating to positive $500 million," he said. "There's still a potential for them to lose money in the holiday quarter, their best quarter."
—By CNBC's Bruno J. Navarro. Follow him on Twitter