Latency is not -as you know -servo speed -it is signal mismatch.
My own elev setups are done off the model -on a bench with the two servos lying flat, facing each other and the arms first positioned on the splines to make for identical "0" centers .
With my DX7 this is so far -spot on every time with any of my servos - sometimes I have to select arms to use but I always start at 0 both servos
then I watch track thru full throws - - - I don't use any servos except JR and JRsport so obviously -I can't speak to any other brands .
This "pair" is put on the model ,then all other adjustments are done with linkage or throw settings - no re-centers - no mismatching of relative end points -no sub trims
This takes more time than fiddling with electronic correction devices but so far -it is still the most accurate method I have found.
the electronic sub trimming methods never worked well for me -
how you can get matched travel and throw speed with mismatched electronic setups is beyond my puny skills.