It would be useful to have in the List of configured adlists a column with the number (quantity) of domains (and size?) added by every list.
Now the columns are: Address | Status | Comment | Group assignment | Action
The number of domains would help in finding a excessively big list or an empty one.
At the moment you see the number of domains if you run a gravity update (pihole -g) or via the web interface. But likely there will be more information in the webinterface in the future: