There should be an easy way to comp between track versions. At the moment there isn’t without bouncing the track versions down. A master comp track that stays fixed between track versions should be an option to enable and you should be able to select what audio from what comp or takes to send and put there like in Pro Tools but with the Cubase track versions changing underneath the master comp track.
There should also be a splitter track that you can insert between lanes to prevent the Comp Tool from comping above the splitter track when the cursor is below the splitter track and stopping the comp tool from comping below the splitter track when the cursor is above the splitter track. This would make it a million times easier to comp takes that were recorded after the track was comped for example, takes from another session or overdubs that were recorded over a previously comped track.
You should also be able to ‘send track versions to split regions’ where it creates a splitter track between each track versions allowing you to easily comp between track versions.