Crack open the bubbly, because retail is back! Just look at the numbers being reported, whether it's J.C. Penney (OTC:JCPN.Q) and Macy's (NYSE:M), reporting respective 3.4% and 1.1% jumps in November-to-December comparable-store sales, or word from American Eagle Outfitters and Zumiez that their holiday sales surged as well. It seems no matter where you look, retailers not named Sears were reporting sales growth.

A strong end to the year

According to the Commerce Department, December retail sales rose a seasonally adjusted 0.4% from the previous month and 5.4% from the year-ago period, while the National Retail Federation (NRF) says the two-month holiday sales period jumped 5.5%, the strongest showing for the industry since the recession.

Shopping mall crowds

Image source: Getty Images.

With an improving economy, higher wages, and renewed consumer confidence, the coming year is seen as getting off on the right foot. "Retail has proven once again that it is the most nimble industry in the economy, able to transform and reinvent itself to meet always-changing consumer demands," NRF President and CEO Matthew Shay said.

But before we toast the entire industry's resurrection, maybe we should take a more sober look at what is transpiring. Doing so reveals that retail remains in some very grave danger.

Bricks-and-mortar is still broken

First, if you look at the reported retail sales gains, you find that most of the increase came not from bricks-and-mortar sales, but rather from e-commerce sales. Using the Commerce Department's data, Internet Retailer estimates that e-commerce sales surged nearly 19% in December alone.

That's borne out by how many retailers' own sales reports played out. Urban Outfitters (NASDAQ:URBN) reported a 3.6% increase in net sales for November and December, with comps rising 2%. While that was below expectations, it is made worse by the fact that bricks-and-mortar comps were negative. The only reason it was able to report positive comps was due to double-digit increases in direct-to-consumer sales.

Smiling couple with credit card lying on the floor and shopping online

Image source: Getty Images.

If we look more closely at what J.C. Penney and Macy's said, both reported double-digit sales increases in their digital channels without actually calling out what its stores did. Considering comps at Macy's rose rather anemically, it's easy to speculate that the bricks-and-mortar channel was down, and probably flat at best at Penney.

And there were plenty of retailers that actually did report negative comps for the holidays, with or without a contribution from e-commerce. Jewelry retailer Signet Jewelers, which owns both Kay's and Jared, said comps were down 5%, while Victoria's Secret parent L Brands (NYSE:BBWI) said same-store sales were down 3% companywide and off 6% at the lingerie chain. And let's not forget Sears Holdings, which said comps plummeted 15% for the holidays.

A great winnowing still needed

The retail industry also remains over-stored. Although hundreds of stores have closed in the past year alone, more will be closing in 2018, and mall operators themselves are now in trouble. Last November, the ratings agencies downgraded CBL Properties to junk status, and even somewhat healthy operators are turning to dubious strategies to hold it together. After Starbucks announced it was closing all of its Teavana tea shops, Simon Property Group sued to force it to keep at least some of them open because it was fearful other tenants would follow.

And the retailers themselves can't use all of the square footage they have available. Kohl's (NYSE:KSS), one department-store chain that did report strong holiday comps, is looking for tenants to take up shop within its stores, seeking out grocers and convenience stores to open up inside.

The 2017 Christmas holiday was certainly a reprieve for the retail industry, but that's all it was -- a respite from the drubbing it's been taking. E-commerce is indeed healthy, but those still heavily reliant on having a physical presence remain sickly. The structural problems of the industry have not gone away, and it's much too early to say retailers are on their way back.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.