You can mix the expression with “Entire Page Loaded” event as well.
I would recommend to show the loader and hide the RG by default and then hide then loader when you are sure the Repeating Group is visible with list count > 0.
Ideally, you can have a loading animation for the progress column as well since Bubble will take the filter into account and then fetch the results, cell-wise. Once your data is populated, you can hide the loading animation.
Another option is to store this metric as a field in your Leadlist_Name table. That way it loads with the rest of the RG. In this case, you’ll just have to ensure that this field is being updated when the Campaign leads etc are being updated.