If you just want to give feedback without any service recovery. perhaps go via the BA GGL Premium team?
I've been mulling whether it is worth dropping them a note regarding the recent changes to the BAEC vs. the onboard service I've encountered over the last year. Out of 12 BA F flights in 2024, 4 had very poor crew and service, which really is an unacceptable number given what they are asking for outright F (airfare wise) or via the new GGL thresholds. I don't want anything from BA, but I think it is worth highlighting why the new changes will make me look at the alternatives because for what is being asked of the customer from 1st April 2025, the value proposition no longer stacks up.

Pilot37