Use your Provider Vectoring ?
you should know that the VDSL-Firmware inside LEDE do not support vectoring.
I guess that the reason are: The versions with vectoring support are not allowed to redistribuable.
But it is possible to extract a firmware with vectoring support from an other Firmware image see here:
Unfortunately my issue hasn't changed yet. Maybe a HW fault? A FRITZ!Box identified the line as VDSL2 17a (ITU G.993.2).
By the way I've found dozens of variants for the DSL configuration but after looking into current dsl_control script only annex setting has to be set explicitly ...
config dsl 'dsl'
option annex 'b'
... everything else defaults to VDSL in it.
Also it's sufficient having default firmware packages dsl-vrx200-firmware-xdsl-a and dsl-vrx200-firmware-xdsl-b-patch. Installing the counterparts dsl-vrx200-firmware-xdsl-b / dsl-vrx200-firmware-xdsl-a-patch as well turns the patch mechanism to save flash memory (generating lantiq-vrx200-b.bin from lantiq-vrx200-a.bin or vis-a-vis respectively) upside down.