That is sad and I understand your reasoning. And nothing I say below should be read as a call to change your current plan.
That said, I disagree that LT has made it self tuning. Default settings for even the one main tunable, md_num_stripes, makes a difference for my 7 disk array. Setting it to 5120 improved my parity by 10% from default. Not sure if this is the best speed:memory option, but i also guess I don't need a full script to test out a few options. But for sure default is slower than tweaked. FWIW, I'm getting same speed in 6.8 tweaked as 6.7 tweaked which was the same speed as 6.6 tweaked
nr_requests I'm not so sure but I did increase mine from default to 256. This is where maybe a script might help to see if there is an interaction. Though my research of what nr_requests does leads me to believe there probably isn't any covariance.
In any case, thank you for all your time and effort. Even if it ends up being the stuff of legend, your contribution to the community really is greatly appreciated.
Thank You Pauven!