Windows Phone 7 was horrible. No native apps, no background tasks, no globally accessible storage, no serious graphics API, no API for audio streaming, no API for anything!
It got slightly better in WP8, but bad impression remained.
Smooth experience, no clutter, no distraction - it just works.
I used an HD7 for years, as well as a 925, because it always felt snappy and "brand new".
I fired up my 925 a few days ago and it still feels fresh, quick, and gorgeous.
You're probably referring to the first party apps which used an entirely different UI framework which was never publicly accessible.
Meanwhile in the earliest days of Windows Phone Silverlight the default blank app in Visual Studio took more than a second to load.
Here’s my old WP7 project implementing both of these: https://github.com/Const-me/SkyFM
Update: the solution in that repo builds a WP7 app using WP8 SDK. Earlier versions used WP7 SDK. I had to upgrade a few things, e.g. replaced Async CTP with Microsoft.Bcl.Async but the changes were minor.
BTW, when original iPhone was released in 2007, it didn’t have any user-installable apps at all, only the built-in ones. The store with the apps was launched a year after the phone.