If Openreach FTTP is soon to be available, it’s got nothing to do with your apparent reduction in FTTC speeds ,if your speeds are less than they once were , it could be ‘crosstalk’ , as more customers take up service in a FTTC ‘cabinet’ , the greater the likelihood that crosstalk becomes an issue , or it could be that your line has a minor defect that is impacting speed, and (AFAIK) if real data from your connection is available ( rather than a mathematical model of the line ) then the speed guaranteed etc. are based on the actual line performance not the guesstimate, so a poorly performing line will see a reduced guarantee, remove the reason for the poor performance, the real world speed improves and so does the guarantee speeds.
You need to look at the router stats to understand if you line is underperforming or it’s simply the new normal
