I've been with WP since Nokia took it on as a smartphone OS. Until then I was a Nokia fan anyway. I liked the convergence they always went for. It was more about having one device for everything than it was about apps.
Now, most Smartphones have got decent cameras, GPS, voice recording, media of all sorts, etc. etc. But I love Windows 10 Mobile, and Windows Phone before that for the customisability of the home screen - small, large, extra large tiles, colour schemes etc. - it finds that sweet spot between simple icons on iOS, and widgets on Android. For me the first is too simplistic, the latter too complex. Since the upgrade to Windows 10, it's been improved upon even more - scaling font size down I now have 4 large tiles across the screen which I think is brilliant.
But...after all these years, I'm actually close to jumping ship for iOS, even though I'm really not a fan of Apple at all.
For me there's one simple reason - Synology NAS.
My storage and media at home (which is a huge collection) is on a Synology NAS and that's not about to change. Fact is that even though Synology has apps for Windows Phone/Mobile, they're crippled compared to their iOS and Android counterparts. You can use the apps so well to manage and interact with the NAS.
I've been waiting forever for some decent updates in functionality etc, but they never come. Updates come, but it's mostly just small bug fixes etc.
I've got an Android phone for work, and I hate it - it's like a toy, fragmented as hell - you never know where a setting is to be found, home screens are a mess - I just can't find myself in it.
I think iOS is boring and unspectacular, but it gets it done well, and clean - and it takes pretty good pictures in the meantime too.
So, it's not the app gap in and of itself (though there are some things missing I'd like), but rather the lack of support for a very specific hardware solution I'm invested in, which is likely to finally put the nail in the coffin of Windows Phone/Mobile for me.
Shame really....
PS: Synology, if you're reading this, PLEASE PLEASE provide a decent upgrade for your Windows Mobile users.