In answer to your question George, I'm after a very neutral base for a very mild specific dish.
The lowest common denominator terminology here is not intended to reflect a down-grading or reduction in any way. It is more so used to describe the process of applying the rule of averages across the most commonly found ingredients expressed in terms of their proportional relationship to a lowest common denominator, being a constant fixed quantity of onions.
It is important to note that I'm not suggesting this list as a recipe. It may or may not be suitable to prepare this ingredient list as a useful gravy, most particularly in relation to spicing. It could end up over-spiced, unbalanced or both or it may actually work. I don't know. The 8 recipes examined use differing combinations in relation to mixed or bought curry powders and single spice powders. Clearly the use of all of the averaged quantities as listed would not reflect any of the actual spice levels from the original recipes due to doubling up of single spices also present in the mixed powders. The use of the main ingredients and other vegetables as listed would not cause the same level of distortion.
Last night I was sorting through pages and pages of old printed recipes from years ago and I found a few other Curry Base Gravy recipes. Abdul's Method, Curried Away Adey Payne, Dan Toombs, The Body Base, and a couple without accreditation, all of which I have used in the past They are all very similar and I feel that their inclusion in the analysis wouldn't really change much. It's pouring rain again today so I might add them to my study and see. It would appear that while Base Gravies are mostly quite subtly different, they are all inherently very similar. Specialty gravies like the "100 Best Baltis Rolls Royce" aside of course.
The reason for my study is because I wish to create a Specialty Gravy which is noticeably neutral and mild and for specific use in a single dish. I know this is completely opposite to the intended use of a universally central base gravy for use in multiple curries.