The TL;DR to your question is a yes.
https://www.aboveavalon.com/notes/2019/10/2/measuring-apples-content-distribution-arm
I know Aboveavalon gets treated with much derision here, but Neil Cybart has done a fair amount of work estimating the amount of revenue Apple's various services could bring in, and he believes they could bring in a total of $5.2 billion in profit by the year 2022. This assumes that within the next 3 years, Apple Music reaches 100 million subscribers, Arcade gets 30 million users (a very conservative number really, considering the sheer number of people visiting the App Store), 55 million TV+ subscribers (well past the 40 million needed to break even), and 8 million news subscribers (somewhat hobbled by the limited number of countries the news app operates in).
In short, Apple can continue to sell to its user base (consisting of 1.4 billion active devices) and still earn a fair amount of money.
The other point is that for all that Apple has done, I wouldn't classify them as a services company. Instead, Apple continues to do what it has always done - leverage its platform to deliver content to its users. It used to be just apps and iTunes content, and has now expanded to streaming music, news and video (and maybe even books and podcasts in the future), but the intent is still the same.
Second, these services also serve to add value to apple hardware and software. While it is true that their content can be accessed outside of the apple ecosystem, I believe that the best experience is still to be had only when using Apple products. Same goes for services such as iCloud and Apple Pay; they literally don't work if you don't have an apple product.
As such, I feel your argument is backwards. You are arguing that Apple's pivot into services is doomed to fail because it is available on so few platforms. I would argue that it is precisely because these services are available on so few platforms that Apple clearly should not be considered a services company at all.
Instead, Apple is building a leading paid content distribution platform. True, the iPhone user base might be small compared to Android, but .9 billion active iPhone users is still a very huge number in an absolute sense, and I believe Apple can succeed simply by marketing to this user base alone.
And Apple is only just getting started.