Deco diving is technical diving, plain & simple. Its DANGEROUS.
According to who?
I know many recreational divers who do DECO diving, have been doing DECO diving for years and they're all still with us... so how dangerous is it?
It is only dangerous if you do not know what you're doing - say like - not knowing how to follow a computer or not knowing how to do tables if that is how you are diving. If you understand basic principles of diving, it is no more or less dangerous than non-deco diving.
As far as the use of "doubles" any redundancy at all is sufficient for Deco diving as long as the total amount of air required for all stops is readily available and a safety margin remains.
Rescue15's configuration seems adequate to me. That is not to say it is appropriate for all "technical" dives, but certainly more than adequate for some.
There is a big difference between extending your bottom time on a wreck in NC at 130 feet and causing yourself to go into a 5 or 10 minute Deco stop... and diving on the Doria.
In the end, the proper configuration for the activity is what matters.