Apple hasn't stopped anybody from advertising, they've only stopped them from doing overly-intrusive cross-app personal tracking. They don't seem to intend to do over-intrusive cross-app personal tracking themselves, so it seems to be a level playing field. So far, at least.
It's important to remember, they aren't stopping them from doing the overly-intrusive cross-app tracking, they just make you actively consent to an app allowing that tracking.
Apple is doing the classic "we don't share with third parties, we just collect a shit ton of data from everywhere and then make people buy our data indirectly via our ad sale services" like google and facebook do today. So it's not shared with third parties, but because of their scale it might as well be in effect size .
It's called App Tracking Transparency and there is a scary prompt when Facebook/others do it. It's called Personalization and a friendly prompt when Apple does it.
They've required consent for cross-organizational tracking. For a single organization, they have only required disclosure in apps (via the privacy nutrition labels).
For instance, Google can still push you to sign into a Google account so they can add all your interactions across services/devices to your profile. They also can still share information between Google native apps for unauthenticated users. This would include if they start to move over apps from other acquired companies under the Google umbrella.
The difference is that I can make an opt-in choice (if possibly a difficult one) on whether I want to interact with Facebook services directly, but I couldn't make a such a choice before on what information Facebook was gathering about me without my consent or knowledge via tracking.
Apple have all of this data (in fact, it's automatically collected and much better quality) because they own the platform on which the data is collected. Therefore, Apple can supply the same services as FB (on iOS only, obvs).
Microsoft did not prevent other browsers from being installed; it just shipped IE by default and made it annoying af to uninstall.
... and entered partnerships with ISPs to have pre-installed listings in IE if the ISP didn't mention a competing browser (p29)
... and entered into arrangements with companies to switch browsers being used (p17)
... and attempted to get Netscape to agree to not compete with Microsoft for Windows browsers (Netscape would be Unix and Mac only if that was done) (p14)
https://www.justice.gov/atr/complaint-us-v-microsoft-corp
There's quite a bit more to DOJ vs Microsoft than just "shipping IE by default".
That a single corporate entity is capable of collecting data does not necessarily mean that said entity is collecting and using that data. Maybe they do! But so far I've seen no evidence of it anywhere from anyone ever.
It doesn't say that in the article and that's patently false. Apple does not have access to Amazon's data about your activity in the Kindle app. Can they potentially track you in the Apple Books app? Perhaps, but if you trust what they're saying, you're presented first with an opt-out dialog about ad personalization.