Smart phones vs Smart PCs
Both are presently useful for different purposes but the operating systems of smart phones carry no “legacy” junk. But too much advertising junk. They are very designed to the shape of one’s activity. Computer OS’s were designed to be compatible with both (for example) games and your private banking. They are good for more extensive tasks (like CAD or programming) where smartphones are designed for and better at shorter tasks (like keeping your contact list or map reading) and being with you.
Most of these functions are inventions that may have a short life. We truly adopt just a few very useful ones, in the long run. PCs will become completely virtual and hardware unnecessary and smartphones is a milestone in that.