I understand your arguments, but I don't totally agree on them
1. When you install 16.5, just keep 16.2 installed. If you use Capture 16.5 to draw schematics you can still netlist to OrCAD Layout and there's no need for "Switch Release", it is only required for Capture since it depends on dlls etc.
2. Answered above
3. The files are automatically updated to the new format. So I would say they are compatible. A newer version of the tool can always open older files. If you open a file and want's to go back - you can always do a File-Save as and save in the old format. Also, it is the first time since 1997 that the file format has changed for Capture - I think that's a long time. Going forward from 16.5 I know that the strategy has changed for Capture so that the file format only will change if you use new types of database objects. Also, going back will strip anything not supported in the older formats.
4. Learning time of going from Capture 16.2 to Capture 16.5 is basically zero. They can use it as is without using the new stuff but just gain from improved stability and enhancements requested for years.
But the main point being is that a new version here also always can work on the old files, but true, they get updated to 16.3 format.