And as we can see from the above context, it's also used to say: "You are insane!" Given it's being used by an admin who has just cleaned a thread of (some of) its weirdism in reply to someone in a similar position.
Nuance is important, but most people aren't bothering with that these days.
I did a stint in Atlanta working on projects throughout the southeast at the beginning of my career and as a fast talking Asian kid with a NYC accent, I got hit with many 'blessings'. I sensed the sarcasm but after a colleague confirmed that people were just politely tell me they disagreed with something or planning to ignore whatever requests were being discussed, I started responding to the 'blessings' by making it clear that I'm dead serious and I only ask nicely the first time
A few people complained that I was too 'direct' but I got stuff done so my bosses were happy and ended up leveraging that into something back in NYC where everyone is 'direct'. I still work on projects throughout the SE and if I get a 'bless your heart' these days, I don't say anything but fully understand that it means the other person is either wasting my time or trying to screw me so I plan accordingly.