Just to let anyone else affected know:
I got this fixed by simply turning off scaling, rebooting the Windows 10 host twice just to be sure, and then set my scaling to the original value.
I use a scaling of 150% in Windows (set in Settings > System > Display), which serves me well to get a decent screen real estate on my MacBook Pro 14'' Retina display, both if I boot Windows 10 natively using Boot Camp or in VMWare Fusion.
After the update I got a popup after booting, telling that the resolution got changed and that I have to log off and on again.
I can't recall the complete history but found the software to be more stubborn than myself, not letting me keep my preferred settings.
I got this finally resolved by turning scaling completely off and rebooting, which probably completed a task set by the installer.
After that I re-applied my custom scaling, and Fusions seems to be content with them.
Small Tip:
When using scaling, turning the High DPI scaling override on in a program's or program shortcut's Properties allows to correct the size of individual applications which don't scale (I use the "Application" setting for a few editing tools which appear far too small in my case).