There's no denying that powerhouse Procter & Gamble (PG 0.29%) has helped turn plenty of investors into millionaires during the company's long history. The stock price is up nearly 6,000% since the 1980s when P&G entered its growth heyday. Its impressive history speaks volumes.

But as the old adage goes, past performance is no guarantee of future results. In fact, it's P&G's incredible past that makes it a less-than-thrilling prospect for investors looking to build a million-dollar portfolio now.

P&G has a little of everything

You may know the company even better than you realize. Procter & Gamble is the name behind Tide laundry detergent, Bounty paper towels, Gillette razors, and Head & Shoulders shampoo, just to name a few of its multi-billion-dollar brands. Indeed, it's the biggest name in the consumer goods business as measured by revenue, driving sales of $80.2 billion in the fiscal year ending in June. Its next-biggest rival is Unilever, but that company's annual top line is only on the order of $56 billion.

There are some clear advantages to being the biggest name in any business. One of them is the sway P&G has with retailers that sell its products to consumers. Another is raw marketing firepower. Depending on the year, deep-pocketed P&G may be the world's single-biggest advertiser, helping maintain and even grow its market share.

But there are also downsides to being the biggest name in any business. These include complex logistics and the risk of being so mass-market-minded that smaller niche players can make a dent in your customer base. For instance, subscription-based shaving supply outfits like Harry's and Edgewell's Billie -- which P&G was looking to acquire just a couple of years back -- have gotten traction that seemed unthinkable several years ago.

Procter & Gamble is addressing the complexity problem. In 2016, for example, it sold the bulk of its beauty business to Coty. In 2018, it simplified its organizational structure by creating six distinctly different divisions, each with its own CEO who has the full authority to manage that operation. And the company's been shedding unnecessary and obscure brands since 2014. All of these moves were meant to undo the bloat that so often comes with years of successful but scrutinized expansion.

The burden of sheer size

That said, none of these efforts change the fact that as a long-lived leader in most of its product categories, Procter & Gamble arguably has the least amount of opportunity to grow. It also faces the toughest challenge in doing so -- its biggest competitor is itself.

And the numbers bear this idea out. Last fiscal year's revenue of $80.2 billion was up a modest 5% year over year, but 4% of that growth came from price increases rather than an expanded deeper reach among consumers. Unit volume, or the sheer number of products sold, only improved by 2%.

That slow pace isn't particularly unusual after stripping out the unusual impact of the COVID-19 pandemic either. Fiscal 2019's organic top line was up 1%. In 2018, sales grew 3%, but after factoring out the impact of acquisitions and divestitures, unit volume -- the total amount of product sold -- was only up 1%. That matches the previous year's tepid unit volume growth, when organic revenue growth was stagnant.

Connect the dots: It's tough for a giant to become even more gigantic. Most of the growth levers P&G can pull have already been pulled.

P&G stock is not for everyone

But it's not all bad. Thanks to stock buybacks and the greater operating efficiencies that come with size, Procter & Gamble's bottom line is certainly more than capable of outpacing its top-line growth. The company bought back a whopping $10 billion worth of stock just last fiscal year (more than 10% of the year's revenue), mostly mirroring its historical pace of share repurchases. That's why the stock's price is also certainly more than capable of making better progress than the company's sales.

In terms of actual growth beyond buyback-induced per-share earnings growth, though -- including operating income growth -- Procter just doesn't bring much of it to the table anymore. It can't -- it's just too big.

PG Chart

PG data by YCharts

This doesn't make the stock unownable, mind you. Investors seeking out steady results, a reliable dividend, and reliable dividend growth will do well with a stake in P&G.

All that said, if you're looking for a core name to drive significant capital gains, there are too many other better prospects out there to lean on this one. Procter & Gamble's gotten so big that there's just not a lot of room left for real revenue growth, and the underlying buybacks that have been driving the bulk of the stock's gains aren't guaranteed to last forever.