If sucess is defined as having fish for over 2 years, you would scratch off alot of fish in aquariums. There are alot of people who do not have fish for 2 years, rather they die, get moved, traded or just given up on. I would not base all my decisions on fish by what is said, or polled here. Not saying your wrong about the Flame angel, just that I know alot of people who have not even had their tank 2 years. Not to mention, the majority of people here have realtively new tanks.
So, scientific it is not. But, I agree... Tank raised would be nice. It just will not happen for a while I belive. The basis of your statments above could also be used for Tangs. There are alot of tangs floating in sewers now. There not that delicate, just need special care. Same could be true for Flames... I would try one with no hesitation. I strongly belive, if you give them the right enviroment, a stable tank and a good diet, they will live a long and happy life. Just like the mandarin.. Provide the right food and a good tank, they too will live.
Just my .02