@klanbo I’d disregard the Orbi speed tester results with Fibre900. It always under reports for Fibre900 but was correct for Fibre300 when I was on that service.
Paying more for less doesn’t make sense to me either so If I was in your position and having tried to resolve it through the standard channels I’d log a complaint.
It was the only way I got my Fibre900 fixed. If BT cannot fix it they should offer a lower band service like Fibre500 at a discount for the inconvenience 🤞 (they did this for me but I wanted it fixed instead😀)