The first-party versus third-party argument has been debunked many times. While it can be generally the case, it is not as clear cut as you make it out to be. FL Studio Mobile is far more popular than you may realize. It actually comes for free with the free version of the FL Studio desktop application.
What's more is FL Studio is the most widely downloaded and installed DAW on the planet nearing 30,000 installs per day, totalling to over 10,000,000 installs per year. Unlike GarageBand that comes preinstalled, FL Studio has real users who are choosing to install it. GarageBand doesn't even come close to the size and scope of FL Studio's real user base.
The iOS mail clients have made great strides, but they still fail to reach the rich featuresets of these Windows apps and programs of mail client offerings:
Since Hangouts is also available on Windows with more features, I don't consider the iOS app on par quite yet. Once FaceTime can allow group video chatting, OS screen sharing, and multi-platform support, I will consider it on par with Skype.
I will not deny the fact that the Windows Store is still behind, but that gap has been narrowing considerably within the last few years. Whereas there is now approximately 700,000 Windows Store apps, there only use to be approximately 100,000 around five years ago. By any stretch, this level of percentage growth is much higher than the iOS App Store.
You neglected to note that the current projections and the current sales I cited show the number of Windows tablets sold will be equal to that of iOS tablets by 2020. This year alone, while the number of iPads sold decreased again by about 20%, the number of Windows tablets increased by 20%. This isn't a slight change or, in your own words "finally be[ing] able to successfully catch-up at least a little bit." This is a textbook example of a mass market migration.
You appear to be disregarding your initial comment about scaling:
Scaling now is no longer grainy or dysfunctional in Creators Update. Unless you are speaking of antiquated desktop programs from before 2000, traditional desktop programs now respond very well to scaling. If you need a button a certain size to facilitate in pressing it with your finger, simply increase the scaling to suit.
And if there is a program that was poorly written for DPI scaling (these are usually programs from over 15 years ago, where they used magic numbers to hard define the DPI scaling), use the built-in virtual touchpad. The virtual touchpad is very fast and sleek, and in no way unwieldy. Either way, in exchange, the amount of functionality in a traditional desktop program versus the best apps is more than worth it.
"Slight" is an understatement: the Surface 3 had under half the single-core performance of the best Core M product at the time. Its multi-core performance was a fair deal behind as well, which is now well under half the multi-core performance of current generation Core M.