Updated March 28, 2016 12:06 a.m. ET

Apple Inc. AAPL -0.43 % fired a broadside at what remains of the personal-computer industry last week, when marketing chief Phil Schiller claimed the company's new iPad Pro is aimed at anyone still using an old PC. It is a wonderful notion—imagine iPads raining down on the users of 600 million PCs more than five years old.

Still, it isn't clear Apple's iPad Pro can deliver on that promise—at least not yet. For one, it is missing some tools essential to PC-like work, most notably a mouse or a trackpad. Moreover, Apple diminishes the tablets' utility by making it harder than it should be for creators of workplace software to make money through its App Store.

As its competitors, including Google Inc. and Microsoft Corp. MSFT 0.44 % , race to create hybrids of tablets and PCs that can function as either, Apple is missing a golden opportunity to dominate the touch-based world it pioneered with the iPhone.

Sales of PCs are declining, but they are still a big market, with roughly 280 million sold last year, most to businesses. But the iPad Pro is hardly a laptop replacement. It has flaws that Apple executives once argued are deal breakers for doing "real work" on a computer.

In January 2014, when competitors were introducing laptops with touch screens, Apple's head of software engineering, Craig Federighi, told MacWorld that "it's obvious and easy enough to slap a touch screen on a piece of hardware, but is that a good experience? We believe, no."

Eighteen months later, however, Apple offered something remarkably like what Mr. Federighi had criticized—a touch-screen tablet with a keyboard. In its current state, the iPad Pro has received mixed reviews. The Journal's Joanna Stern lamented the lack of a trackpad, which highlights the oddity of using a tablet to replace a PC.

Touch interfaces can be intuitive and sophisticated, but mice and trackpads persist because having to touch your screen for even the most elementary actions, like selecting text, can be both clunky and tiresome.

There is a second reason why iPad sales fell 23% in the fiscal year ended September 2015, from their peak two years earlier: Apple has put onerous constraints on the makers of software whose apps are key to the success of the iPhone.

"Whenever my friends say, 'Denys, we want to make money on the App store,' I spend a lot of time trying to tell them not to do this," says Denys Zhadanov, head of marketing for Readdle Inc., a Ukraine-based company that has had best-selling productivity apps on the App Store since the store went live in 2008.

Mr. Zhadanov says Apple makes it hard for developers to connect directly with users, or to encourage them to buy upgrades. This means app makers can't reach users through mailing lists, critical to generating repeat sales and marketing other software and services.

As a result, apps that Readdle first released in 2009 generate no additional revenue from the company's most loyal users. Readdle says the lifetime value of those customers can be as little as $2.

"Most of what's wrong with app distribution feels like the result of bad decisions made five years ago that are now taken as gospel," says Michael Love, founder of Pleco Software Inc., which sells Chinese dictionary apps on the App Store.

Apple's App Store offers some advantages for software makers, particularly big ones like Microsoft, which offer free apps that complement software sold elsewhere by subscription. In-app purchases help game makers sell extras and upgrades, though they have to give Apple 30% of their app store revenue.

None of the challenges facing the iPad are insurmountable. Indeed, the question of whether an iPad should replace a PC may be a red herring. Tablet computers' potential will only be realized when developers, users and Apple itself combine hardware and software to let us do our work in a totally different way.

To understand what this will look like, take a workplace that never had PCs—the construction site. PlanGrid, which replaces paper blueprints with an app that displays them on iPads, is a good example. Free of workflows shaped by a PC, tablets are a natural fit, says Tracy Young, co-founder and CEO of PlanGrid. She is agnostic on the device; PlanGrid supports just about everything flat with a touch screen, from iPads and Android devices to Microsoft's Surface tablets.

It is hard to remember that it was ever otherwise, but our work isn't spreadsheets, documents and presentations. They are merely tools for completing that work. As devices and interfaces evolve, we can find new and more direct ways to accomplish these tasks, from live dashboards that replace presentations to photos, sketches and visual communications in place of things we laboriously describe with words.

That is why I still think tablets—and the iPad, if Apple is lucky—will ultimately replace nearly all PCs. But rhetoric about an iPad Pro as a drop-in replacement for a five-year old PC—now just one part of a much larger network of habits, software, infrastructure and dependencies—is folly.

—Follow Christopher Mims on Twitter @Mims or write to christopher.mims@wsj.com.