What made the iPad successful is that it works, and rather well. Apple has been making products that work-- specifically, the user understands how to use them and gets the results they intend.

This is a single feature that very few companies include in their products.

Usability is not a trade secret, it is simply not in the culture or preferences of the leadership of microsoft or google to make products with usability. Sony used to, but is more hit or miss these days.

Asking, "what if the iPad had come from Microsoft first" is a question that doesn't work. Microsoft introduced their iPad almost a decade ago, with windows for tablets. It was q flop.

If that doesn't fount because it isn't like an iPad, then the question is like asking "what if an orange tree bore apples?"