> Apple has violated Section 2 of the Sherman Act due to having a monopoly on Apple services?
Sort of. There are two possible avenues of attack here against Apple. And it depends on how the market is defined.
1: if the "market" is defined as you have, which is a "monopoly on apple services", then it absolutely true that Apple does have a monopoly on the specific market as defined by "Apple services", and I would accept 10 to 1 betting odds on that.
BUT, I think it is a bit of a stretch that the "market" will be defined that narrowly. Instead I think that the market will be defined as the smartphone market share of the USA.
2: If the market is defined as the smartphone market, in the USA, then the argument will be that Apple has control of ~50% of the market, in a 2 entity duopoly. It is a common misconception, that anti-trust law only applies in cases, of a overwhelming singular monopoly. Instead, anti-trust law, applies even in cases where there is not a singular monopoly, and the company in question only has significant market power.
Controlling 50% of the market share, is a bit on the edge of whether anti-trust law applies, or does not apply, as according to government guidance. So the case is far from a slam dunk, and I think that there will be interesting arguments brought up in court.
But, even though Apple has less market share than, say Microsoft did, when Microsoft lost their anti-trust case, I think that Apple's actions are significantly more restrictive than Microsoft's was, and thus this contributing factor will push them over the edge into losing the case.
I expect that this case will be a landmark case, that will determine future court actions, and will be even more significant than the microsoft case was.