Thinking a bit laterally here - one of the benefits to BA of tier point runners (or people for whom TPs just marginally swing them in favour of flying at all/flying BA/flying premium cabin) is that it helps sell their cheapest seats - ie, the ones that they are struggling to sell. Under the new system, TP-chasers won't be filling those cheap seats as they just won't move the status needle enough to be worthwhile. So what happens to those unsellable seats?

Long term, I think this is actually a way of boosting the Avios redemption inventory. Under the new model, the BAC is for business travellers, and the Avios ecosystem is for leisure. Perhaps to BA it seems like a better way to generate revenue from low-yield flights while still rewarding their most loyal (ie, price-insensitive) customers.