Microsoft didn't totally remove Aero Glass transparency in Windows 10, but they crippled it in such a way that it became useless for irregular dock backgrounds. Even now I believe you can only natively blur 'square' or 'rectangular' areas/windows/backgrounds.

There was (is?) a 3rd party utility called Aero Glass that enabled the old Aero Glass/Blur functionality in Windows 10 for applications that could take advantage of it, but even though it works it's a 'run at your own risk' type of thing. I think it is also a lot slower - but I didn't actually time it - than what you had in Windows 7.