Can you define a market that Apple has a monopoly in that a regulator should investigate? You've identified current iOS users, but surely that's circular? I don't doubt that iOS market share is super high in some segments, but do any of them constitute a regulated market?
In education the last I heard was Chromebooks are at over 50% of devices in US schools, and that's against Windows and iOS. I'm sceptical Apple have a monopoly in education except "tablets in schools" which again doesn't seem like a whole market.
Identifying iOS users as a target for Apple's monopoly is no more circular than identifying Google-branded (ie. Nexus et al) Android users as a target for a Google monopoly. Non-Google branded Android can, and often does use non-Google apps and stores so that segment can not be considered to be monopolised by Google. In practice the same is true for Google-branded Android devices as it is possible - and not all that hard - to swap Google apps for others.
As to whether I think anyone should investigate Apple and Google I'd say 'no', but that is not what this is about. I don't think Google should be investigated for the stated reasons, but if the EU insists on investigating something I claim there is at least as much ground to investigate Apple as there is to do so to Google.
Where I live - Sweden - Apple does have a large presence in schools. The situation with regard to IT in Swedish schools seems to be that there is money, but no plan. This makes it possible for 'driven' people to steer their local community in the direction they deem to be the preferable. Many of these 'driven' people have a marked preference for Apple products.
I'm not so sure that Google actually does have the same circular monopoly power as Apple, because really it's just about lock-in and - from experience - moving from Android to iOS is really easy. You don't lose any data and everything is cross platform by default. Going the other way by contrast, you'd have to deliberately move things into third party cross platform apps.
I'm also not sure whether that would count as a monopoly if they did have sufficient lock-in, given their vast market share - as a hypothetical. I guess probably yes.
I'd agree that neither should be investigated, but I do disagree that Apple have as much grounds to be - they just don't have the market share.
I was probably too simplistic on education, it's a difficult issue for sure. My ICT teacher in school used to have a pretty big budget and spend it on toys because he got Windows hardware/software so ridiculously cheap. Microsoft had made the ICT curriculum in the UK entirely based on learning how to use their software and apps. All their stuff can be obtained between free and really cheap for students from school to university, and it's pretty much always the standard expectation to use it. And then you have iPads and Chromebooks taking over, probably not running Microsoft apps and probably like you said with no real plan. It's interesting and probably broken, but there's probably no monopolistic player there.
In education the last I heard was Chromebooks are at over 50% of devices in US schools, and that's against Windows and iOS. I'm sceptical Apple have a monopoly in education except "tablets in schools" which again doesn't seem like a whole market.