I have tried all those things many times.I'm a bit busy today so i can't reply to all the points you mentioned right now but i suggest you give Dirac a sensible try first (limit magnitude correction to transition frequency, only measure what needs to be measured, adjust target curve if you run out of headroom) before we continue this discussion
I think the Audioholics video about a different "magic box" DSP highlights the issues around proprietary filter design.
In the Audioholics video, the RBH guy claims, and this is a paraphrase, "We found a new place to measure the DSP autocall and WOW, the results are amazing, but we are not going to tell you our secret measuring technique."
I am not sure what DSP they have but if its like Dirac, hidden filten design, then they are 2 times ridiculous. they are saying
1. Hidden filter design
2. Hidden "secret" measuring technique
I am heading to a studio for a mega church today, My job is to bring the tracks and score sheet to subjectively rate the system based on a scoresheet I have spend much time crafting and changing. I have 1 day today to get it done today with my team, we can not really on hidden algorithms or as RBH claims, "non-standard measurement positions" that bring "magical" results.
I have found that 1 position measurements work best in my room set up.