Per updated guidance for its upcoming 2024 fiscal year, issued on Dec. 13, Pfizer (PFE 0.55%) has a bumpy road ahead -- at least for now. Amidst rapidly weakening coronavirus product revenue and significant cost cuts billeted for next year, the drugmaker's annual sales of more than $100.3 billion in 2022 are undeniably a thing of the past.

But as smart investors know, betting against one of an industry's capstone companies can mean missing out on returns over time. So is there still a long-term investing thesis for Pfizer, or are its best days in the past?

The case for not investing

Let's take a beat to appreciate why it's perfectly reasonable for investors to be having doubts about this company's chances of being a good purchase, given its upcoming challenges. Management is expecting that the 2024 top line will be around $61.5 billion, at best. Given that it's anticipating a maximum of $61 billion for this year, the story is clear: There's no growth coming, at least in the near term.

As mentioned, the reason for the stagnating top line is that demand for its coronavirus vaccine, Comirnaty, and for its coronavirus antiviral pill, Paxlovid, is collapsing now that the most intense phase of the pandemic is over. It's very unlikely that demand will return anytime soon.

But what about potential growth from other new medicines in the pharma giant's gargantuan research and development (R&D) pipeline, which currently boasts 83 programs? Even without the decline of coronavirus product revenue, the company would only grow its sales by a maximum of 8% on an operational basis this year. That's including the launch of at least 10 programs, split between new medicines and expanded indications of previously approved ones.

The troubling conclusion for investors is that if Pfizer wants to expand at a faster rate, which is to say a pace that would imply some real upside to the stock, it needs its pipeline to be even more productive. Even for one of the world's largest pharmaceutical companies, it's hard to do much better than it already is on that front; it has 23 programs in late-stage clinical trials.

So it looks like in the next few years, it will be quite difficult to maintain its current less-than-snappy pace. And that implies it'd be better to invest elsewhere.

Why now is the right time to start loading up on shares for the long haul

Keen readers will note that the bear argument against Pfizer is centered around its short-term performance. The bears aren't wrong: The doldrums are here, and they won't be leaving for a while. But after zooming out to look at the next decade and beyond, this company is very likely to be a decent investment for the right kind of investor. 

As of Dec. 14, Pfizer's acquisition of Seagen, an oncology drug developer, is wrapped, and starting next year, its new oncology division will be formally initiated, packed with twice as many programs as before. The deal, inked earlier this year for $43 billion in cash raised via taking out debt, is part of the company's grand strategy to revamp its pipeline over the next six years or so.

Via a combination of acquisitions, licensing of pharmaceutical assets, advancing new programs in its pipeline, and expanding the indications of existing medicines, Pfizer aims to add around $45 billion to its revenue by 2030. It'll also be able to realize at least $1 billion in cost synergies to boost its profitability along the way -- and that's on top of the $4 billion in cost savings expected next year from other economizing initiatives. In short, this is going to be transformational for the company, but it's going to take a while.

After paying off the debt from the Seagen acquisition, management plans to start diverting more of its capital back to investors in the form of share repurchases and dividend payments. At the moment, its forward dividend yield is at a high 6.1%, which means now is an attractive entry point for long-term holders. When paired with its Goldilocks neither-too-pricey-nor-suspiciously cheap valuation, at a trailing price-to-earnings (P/E) ratio of 14.5, the case for buying shares now looks even stronger.

Of course, none of this is to say that Pfizer is going to be a rapidly growing business. The point is that it has a long runway ahead to continue throwing off cash while likely retaining most of its value -- and the price is right.