There are two hidden issues here that make me think this is a change for the worse for many of us.
1) On routes where tax was lower than RFS fee, you previously had the option to pay the fixed Avios price and the actual tax. This is now gone. E.g. have just priced PMI-LCY which used to be 6500/7500+£9.70, now it is 6500/7500+£17 just like the outbound. Hidden price increase.
2) Refunds. When you used to have the flat rate and the option to pay reduced Avios for more cash, the cancellation fee was always capped at the amount of the taxes and the additional cash paid to reduce the Avios element was always refunded. E.g. continuing the example above, PMI-LCY was 6,500 + £9.70 off peak but you could reduce this to 2,150 + £35 + £9.70 (and effectively buy Avios from BA at 0.8p) and if subsequently cancelled the fee was capped at the amount of the taxes, £9.70 and you got the 'cash' element back in full. I have a feeling cancelling one of these will result in a £35 fee whenever more than that has been spent, which obviously makes the higher Avios/lower cash options more attractive, but as we know these are at a value of less than 0.5p/avios spent.
As someone that books 50 of these a year it's a big negative impact for me personally.