This is all just posturing
They are shaping up for the real battle: 800MHz. Whihc Ofcom has said will be allocated/sold/auctioned some time before 2022.
BT wants to be free of caps so that it can buy the 800MHz. Ofcom only cares about looking good to government by getting as much money as it can out of telcos. So Ofcom wants as many bidders as possible.