You should read over the antitrust laws and precedents. They cover all the ground you're discussing. You may be surprised by what they contain. For example, simple market share percentages like you listed are only one of many metrics used by regulators to establish whether a company has a dominant position in the marketplace. You should also read the Apple section of the Congressional report I linked.
I've just read some of it and can only conclude that the people in the justice department have no understanding of the computing industry at all. The sound like people who come to the party late and complain that the DJ didn't play their favourite records.. because they played them all when they weren't there!
Things that we basically fought for in computing for over 40yrs.. things that have been achieved they just gloss over as if its some terrible negative. Its makes for crazy reading.
In short, competitors have not been able to break the "duopoly" (clever how they talk about the OS's rather than the manufacturers, where you see tons of handsets) because they dont give the people what they want! They have ulterior motives. FB doesnt want to make a handset that has privacy, Amazon wants to sell you stuff, MS just wants to make a handset so no one can block it.. no one actually wants to make a handset to you know.. make a good handset! Apple ties in its hardware design with its OS's to make a better product. SO thing they see as negative are actually better for the consumer. But they gloss over that stuff.
Apple has consumers first.. even google know that they have to make customers like stuff and hide all their ad fleecing in the background. Make GOOD THINGS! And you can compete.
Also, lock in isn't a bad thing! There's a reason why there are only a few OS's.. they are ridiculously hard to build and maintain! After 40 odd yrs of computing there are literally only 3 main stream fully featured OS's in the world, MacOS, Windows and Android. All paid for by various "lock-ins" (being tied to Mac Sales, tied to Enterprise Windows software or Ad sales in googles example). You cant do it any other way. Its too damn expensive.
Without building tools that link to each other you cant do it. Also, its what customers want. They want the links.
Furthermore, you cant just be compatible with everything because you end up with things that dont work well (Windows..).
This is all computing 101.
The legislators are being gamed by various lobbyists and organisations. I wish they took the same angles with net neutrality and cable companies... but oh .. it really depends who's paying there lobbyist doesnt it?
And actually thats the point, the narrative is written by the one who pays the most to get govt to change the rules. Everything they say in the document can easily be argued against if you understand the history of computing.
Apple and googles dominance is because they actually put the hard work in to make things people want to buy! Apple are ahead of the game because they actively try and make the best products. Thats not how other businesses operate. It really is more simple than some nefarious unfair activity. People are just good at making things and want to be better at it.