SC is frankly a piece of piss to get: you fill in a questionnaire and there's some basic checking.
DV on the other hand really is a proper background check. Back when I did the then "new, shortened" form, it was in excess of 50 pages. For my face-to-face interview (mine was a simpler one so only took a shade over 3 hours), my interviewer pulled out her own copies of my bank statements to compare line by line.
They interviewed friends and family members as well as previous bosses from up to 5 years ago.
Because of certain other add-ons we required at the time, we even had to submit our holiday plans' flight paths to ensure we weren't crossing airspace that was considered too unfriendly.
The whole process took several months to complete. It is not something I would ever care to go through again, if I am perfectly honest - the benefits simply are not worth the hassles.
And yes, financial institutions have checks that fall somewhere in between the two extremes.