Hi,
Unfortunately there's no way (yet) to get statistics per activity type in the logbook. That is what you are asking about, right? For example, looking at your total mileage or climbing in a month?
You are right that you could combine all your GPX/TCX files for biking into one file and then do some analysis using other parts of TopoFusion. This would be a way to get some summary statistics, but it would be a little tedious for sure.
Per activity stats is definitely on the 'todo' list. Thanks for the note.