Every installer has the option to set the VST location and data separate, there are a few that have a folder with settings included with the plugin, but not an issue.
I have even set vendor folders for every plugin :

The only plugin file I have had to manually more because the installer did not allow a path to be set is Waves and their actual tech notes suggest if you use a custom folder to simply move the waveshell file to your preferred location.
The only plugins I have also had issues when manually moving plugins around would be Native Instruments because they rely on registry paths to locate plugins for things like Kontakt libraries but this is a simple fix if required.
Most plugins will be fine to move but I always suggest to copy/paste the plugin and not move it. This was, when you do an update you can compare the date of the plugin in your custom location.
VST3 fixes all this because most users these days don't pay attention to installers and just blindly click next...next... to install things and then only after making a mess want a duct tape solution to fix everything. VST3 is now in a fixed location to solve this for users.