In Microsoft's case, the free and privileged position of IE was specifically chosen to prevent the success of a competitor (Netscape) whose product created the potential for cross-platform applications (enterprise, early web applications). IE deliberately implemented some things counter to the specifications in order to be incompatible with the spec (and thus spec-conformant browsers) forcing developers to select their target platform. IE's substantial market position meant that more people supported it (thus all the sites that were IE-only, and some still are because banks and governments suck at IT). MS spent hundreds of millions (if not over a billion, it's been a while since I read the reports on the subject) to give away a product that would cripple a competitor's position. Netscape, though, wasn't the only target of MS's action. By doing this, they helped ensure Windows dominance would continue. Enterprises considering, or using, other operating systems but wanting to advance the state of their IT systems (that is, adopting web-based solutions) would find themselves in the same conundrum. Implement to the standards and use any OS, or implement to IE and support one OS that was already dominant within the corporation.

This worked to effectively reduce the potential market position (in businesses and for consumers) of alternate OSes to Windows.

Of course, that's not the only thing MS did. The full report of the anti-trust case was pretty interesting. There were many things MS did beyond just the browser. They favored OEMs who exclusively sold Windows-based computers with lower OEM pricing, but if they attempted to use another OS then they were threatened with increased licensing costs (this was a large part of what killed BeOS's momentum).

While many people remember and focus on the browser, it was only one piece of the whole case. To draw a comparison, you'd need to demonstrate that Apple's Safari-only (or really Safari + limited WebKit-only) policy is taking advantage of its substantial market share (currently iOS is sitting at something like 55-57% market share in the US, so it isn't actually that substantial a lead) to harm its competitors. And you'd have to place that in the context of other abuses of market share position.

Forcing WebKit-only enables Apple to selectively disable key features in all browsers on iOS, preventing web apps from competing against FaceTime (WebRTC, Fullscreen API) or iMessages (Service Workers).

Instead they need to go through the App Store, driving up development costs (the Swift learning and/or contractors) and decreasing potential competition.