With Oracles, the answer will be invariably positive. I'm sure many will disagree (and I am not talking about Doreen Virtue or Angel decks) but I think I choose my oracles carefully and try to go for ones that have an intelligently thought out system.
I hope that's not a global rule or anything because I'm working on an oracle based around existential philosophy and the only real reason I'm not making a tarot of it is because it's an uneasy fit that would feel contrived and gimmicky.
While I have seen plenty of oracles that were little more than unstructured collections of affirmations (an in those instances, why wouldn't one just use a desktop calendar?), I believe that there's plenty of scope for workable and insightful structured systems in oracles.
Even so, it is invariably one person having come up with something in a vacuum.
You say that as though it is a bad thing
But seriously, I don't think there's a rule saying an oracle has to be a solo effort. And I don't think we've proved that Tarot wasn't.... meaning that "one person" can still contribute something of worth.
and "in a vacuum"? Hardly. We're leaning on some very old establiished traditions here. If I were to claim that my oracle were created by myself in a vacuum, I wouldn't be being honest about the hundreds of years' worth of of contribution to a strong and timeless concept that is the basis of inspiration there.
And I guess this leads my to a question that has been on my mind lately... is evolution a relevant concept with Tarot? Does it adapt and improve and change with time, or is it perfect and fixed and only diminished by tinkering with it? Tarot Intelligent Design VS Tarot Evolution, if you will...
... and my own conclusions are that evolution is going to be necessary - at least for my own implementation. I don't think deep wisdom stopped a thousand years ago. I don't necessarily believe that all the concepts that went into the tarot are still the best we can come up with.
I think there's been a lot of great thinking in the last hundred years that is as valuable and insightful for speaking to the human condition as any of the primitive religious concepts in RWS, for instance. While I personally love the Tarot framework, which has been a lifelong friend to me, I feel that there's a lot of aspects to life in the 21st century that is passed over in favour of archaic and quaint concepts from medieval times.
Just as we don't have any authoritative last word on tarot origins, we also cannot truly be sure whether the system was intended to be updated with changes in society or if it was designed perfect and unchangeable. And to avoid rocking the boat, I'm making mine an "oracle", which I truly hope doesn't have to be shallow or saccharine in nature.