iOS is certainly more developped that Windows Phone 8.1 (the way they handle notifications with direct responses, their very informative lock screen, their actual toggle switches for different functions like Wifi or data). But those are things that can easily be added with time on WP (lets not forget we're about 3 years late from iOS).
That being said Windows Phone is different, yes, but not user unfriendly. Obviously if you're an iPhone user, you might be more confused on Windows Phone as opposed to Android. But the opposite is also true.
You can't do these kind of comments on an iPhone centric standpoint. If someone who has never touched a mobile phone grabbed a Windows Phone for the first time, I don't think that person would be more confused than another platform.
On the other hand, the WP environment CAN become less user friendly when it comes to apps. Most apps are being made for iOS and Android and, sometimes, for WP and sometimes abandonned (*cough* instagram *cough*). We do sometimes have to go through more hoops to get certain things. For example, on iOS, you can just download the YouTube app (or any other official Google app). On Windows Phone, you have to check out all the unofficial ones to see which one if more trustworthy and functionnal. Same for Instagram, Pocket, Wikipedia and so on. A lot of banks, news papers, radio stations, etc. don't have any apps at all. So, especially for a neophyte, that can be confusing especially if you have to use a third party app.
But that's not the OS's fault... so the OS itself, no, it's not less user friendly.