I think this is a healthy problem to have, I think it could spur some innovation and focus on getting some technology to the iPhone in 2019 that might have taken til 2020 or 2021 to adopt.
Also, in every company, two big risks are "inventory levels" and "payroll." Even for a company with tons of hoarded profits, you have to always watch both. Apple is one of those companies that Steve Jobs knew should "think big" but "act small" as far as acting like a "small company" when purchasing and dealing with inventory levels.
So, we know that they've already adjusted production and shipments (inventory), and now they're at least being cautious with hiring (payroll).
No matter how much profit is built up, you have to play by the budgets you have for this year. So, I'm sure they're thinking about how to adjust to a slowing of revenue, at least for the first two quarters.
I do agree that Apple is making iPhones with materials and finishing that make it last well over the 1-2 year cycle that people usually upgrade. iPhones 5 years old still work fine for people who just want the phone to work, and have the basic e-mail/texts they normally rely on. I also agree that, once a phone goes well above $1,000, like $1,200-1,400 for the top top model, it becomes a bigger decision. I'm an early adopter, so, I try to forget about the price and hope that the monthly charges aren't too high!
For people who say that Apple hasn't created a product under Tim Cook, I kind of disagree. I get that products may have been planned out 2-3 years after Steve had to leave. But, AirPods are extremely well made and have captured the market, even with younger kids who gravitate towards non-Apple phones, still love AirPods. Also, Apple Watch has really changed and made more meaningful upgrades the past two generations.
HomePod probably needs a major version 2 upgrade like the Watch needed.
I love the new iPad Pro, but even those get very close to $2,000 or more if you want the really top models, and that's hard to budget for.
So, there are challenges and potential for growth on the horizon. Can an iPhone incorporate enough new technology and features to really give them enough of a gap from competitors that they're the clear choice? I think the competitors have caught up a little bit. Also, could they make a really low-cost phone for the China/India market that competes with home grown phones and cellular plans?
One thing about Tim Cook. Could anyone be as innovative and creative as Steve Jobs? Steve probably hated companies that had huge "tech" divisions, but never produced anything. He found a way to sort of mash the heads together of technical departments, and creative departments, to focus on single products that disrupt the marketplace. In fact, I think a lot of the more "rude" or crazier things Steve did were a refusal to allow Apple to become like those companies who never make anything, and he probably had to take some extreme positions on corporate issues to make that point over and over.
Tim knows product chain management, and, has a conscience about how a company should act. Just think how much worse things could be, if you didn't have someone competent like Tim Cook to take over. If the smart phone market has truly plateaued, and we're looking at a race to become a "commodity," then I think would be as much a challenge for Tim Cook as it would have been for Steve Jobs. Can Tim make some magic happen? We'll see I guess!