So if I am picturing this correctly, you have your main breathing gas with an octopus plus a separate, redundant pony bottle with it's own regs?
You already have an octopus, the fact that it is attached to its own first stage and own tank is just a bonus. Think about it, the octopus came around with the mind set that every diver in the water would have a completely redundant set or gear to breathe off of in the event of a major failure. The diver would have his own equipment plus the redundancy of his buddy's dive gear with an octopus. (Whether the donor or receiver breathes off the octopus is a moot point for the purpose of this discussion) That level of redundancy remains today and in many cases has been raised by divers wanting to be self-reliant and carry their own redundant set of equipment (like your pony bottle system). While it is nice to have in the sport diving world and more necessary in the tech/cave world, it is in the PSD world where you are in the water alone a majority of the time and need the separate redundant system that is not present in the form of a buddy's equipment.
With the system you have described, you have met and surpassed a level of security offered by an standard octopus off of the main tank. There is no reason to have it still there. If there was we'd all be sport diving with two or three octopuses (octopi??) just to be super-safe and we just don't. Surface Supply divers don't wear and octopus on their bailout because the chance of it malfunctioning and draining the bailout is greater than the chance of the band-mask/helmet failing. You said it yourself, the risk outweighs the benefit with the pony system present.
Remember in PSD you need a clean configuration.., more is not always better. Stay away from stuff that is not of the utmost importance, like a second octopus or long hoses.
How are you carrying your pony? Back mounted? Slung to pass off? Most teams I have dealt with over the years have tried to stay away from slung tanks on searchers as they tend to be poorly placed during the zero-vis/belly crawling searches. Some will back mount the searchers and sling a pass off bottle on the rescue diver/standby-diver/90% diver or whatever you call them.
The important thing is get a set up a gear configuration, make it a standard for the whole team so that everyone is exactly the same and train, train and train some more with the new config until it is second nature