The only thing it illustrates to me is that, by and large, we can't agree on anything, not even the simplest thing!
You got that right. For example, you have clearly ruled out the korma as a 'benchmark' curry and I would suggest you are absolutely wrong on that.
I would say that the korma is one of the best, if not the best, tests of the adequacy of the base sauce. Why? Well, we know that the korma is base sauce + coconut + cream + sugar, and sometimes almond powder. In fact it is probably the only curry we really know FOR SURE how the BIR cooks. There's no technique involved to muddy the waters, just lob it all in a pan and boil it down to the right consistency! Therefore as we all know what coconut tastes like, and we all know what cream tastes like, it leaves only getting the base right to match the takeaway. That is, the base is the defining factor in this curry, much more so than any other BIR curry.
Of course this assumes that we are all familiar with the BIR korma, and I'd have to say I am not as I find it a nauseating concoction, but it is probably the best selling curry from BIRs, despite what they claim about CTM, and therefore is more likely to be made by people on this forum than, say, a madras which might be outside a lot of people's comfort level.
It therefore seems to me to be the ideal candidate for the benchmark curry, something which I posted about some two years ago I think under the title of 'is this a true test of a BIR base' or something like that.
To summarise why I suggest this is THE candidate for a benchmark curry:
1. We know for sure how BIRs make this curry, and, from what I have seen, the way this one is made is very consistent from BIR to BIR, both in technique (lob it all in and stir), and in ingredients. I don't think that can be said of any other BIR curry.
2. The defining factor is the base sauce as all the other ingredients are known. Therefore match your korma to your BIRs and you know you have the base sauce sussed. We can then go from there.
3. There is no hidden or hard to master BIR technique involved in its making.
4. It is one of, if not the, most popular curries from a BIR and should therefore be likely to be made and tried by more people including the chilliphobes.
5. There are no extra spices added at the curry cooking stage so we don't have to try to guess what they are!