In the PC world, it's a mistake to argue whether or not Apple can beat Windows because it doesn't try to. Apple competes with Dell, HP, etc., not Microsoft. Apple can't beat them all combined but it can definitely beat many, maybe all, of them individually in terms of profits.
It's the exact same with phones. Apple doesn't need to sell 95% of the smart phones out there. It can and will make a bundle just selling 10%.
Apple (OS X) can't beat Windows (Microsoft) but it's not because Apple is not/was not trying.
Apple does compete with Microsoft and would love to be the dominant OS. If they were, their profits and market share would be stratospheric. They're doing extremely well selling just 5% of PCs but can you imagine how well they would be doing if they were selling 95% of them?
The same applies to phones. You're right that they would do well selling just 10% of phones but the goal of every company is to get 100% marketshare.
Clearly, that's not going to happen but let's not fool ourselves: Apple and Google are in a cut-throat race to be the dominant phone OS (in marketshare terms) because the number one is more handsomely rewarded than number 2, in any market, and both companies desperately want to be number one.
If Apple were trying to make OSX the OS with the highest market share they would license it out. They are clearly not pursuing that strategy. If they wanted to sell the most computers in total, they'd lower prices to compete with Dell, HP, etc. They do neither.
I'm sure they'd like to see their market share rise, but their business plan in computers is to own a small but high markup slice of the market, knowing that in doing so they will not be the volume leaders.
Apple is doing well out of their 5% marketshare, because they have an expensive 5% of the market. If they were to serve 95% of the market, they also have (at least) the cheapest 45% of the market.
It's the exact same with phones. Apple doesn't need to sell 95% of the smart phones out there. It can and will make a bundle just selling 10%.