Short answer: Yes, it is normal.
Why is a longer answer.
Steinberg themselves invented the VST3 (and earlier) format and the format says all VST3 plugins should be in the Common Files\VST3 folder …yet they choose to put their own in a different folder specfic to Cubase (or WaveLab etc). Don’t know why though it may be becasue they’re not accesible to other programs?
They are dedicated to Steinberg products only… internal plugins so to say…
Heh, just theorizing (and adding) that as you wrote! Cheers.
Thanks a lot guys! 
It was the Waves plugins for me. they just stopped working and leaving cubase hanging at the scanning vst3. going to try and re-install all waves plugins and see what happens
I had this same problem recently. fortunately I magically got cubase to open after an hour of waiting and multiple “not responding” warnings.
I couldn’t have fixed it by disabling plugins either, because I accidentally saved a folder path that was my entire hard drive and it wouldn’t let me change paths when I opened it with disabled 3rd path plugins. ( a feature that needs to be implemented)
By getting rid of that path and deleting the last installed plugin I was able to resolve my issue- but the consequences would have been grave had I not been able to open cubase that one time.
creating a backup of your system every once nd a while is so important, because I have SO many plugins having to redo it all, would literally take me a month or more.
VST2 plugins are obsolete since more then 10 years…
there will not be any compatibility fix for VST2 anymore
searching and checking .dll files doesn’t help either to make a system scan faster… that’s why it changed to .vst3 and all VST3 plugins should install to a standard file location, at least with a symbolic link
The switch to VST3 should make it all more stable…