1) If you are having issues installing it, sounds like you need to check your installation media, you using torrented iso's, using official windows iso's put onto usb drives using windows official usb tool, using the "windows upgrade tool", using official windows iso's, and the upgrade tool, of all the installs ive done never had a single issue.
2) i'll take your word for it
3) some of us like dx12, and like to use our fancy new hardware to its best benefit. Another plus for developers is it has bash. it has a bunch of features not available with older windows, just depends if they are for the individual user. multiple desktops(super helpful for multi tasking professionals), bash (yes you can run linux code natively in windows 10) , being able to store your cd keys linked to your ms account, so when you upgrade you dont have to buy a new license to transfer, edge, windows defender is there by default (i disable it as i despise antivirus) but for the avarage joe having a pre-installed good antivirus is a plus, it does a bunch of stuff that the older operating systems don't, i see that thrown around alot, "it doesnt so anything new besides dx12", which is not factual.
4) since when has an operating system ever been...... FASTER than its predecessor?