Yeah, blanks can indeed be powerful at filling some nooks on the board but also meant to be dangerous and annoying when they and up in your hand or deck or if used haphazardly.
It is intentional that smite doesn't trigger when heretic spawns on a PB tile. If it did, I think it would be maybe too easy to use and very much on the too good spectrum on power. Now you need to do a bit of planning to actually use that properly.
It actually is already shown on UI. It says "pick your rewards" if you've got multiple and after picking the first, it'll say "pick x more" etc.