It's back to Long Haul vs Short Haul. Only BA has short haul passengers in T3 and it a much higher quantity. As for not missing the CX F lounge, it sounds like they were turning away the J lounge as well, which leaves the options in T3 much more degraded for me (no champagne in AA or QF, and I've been in the BA J lounge once, years ago, and remember it being horrible).

When we (as gold at the time), presented to the CX lounge in July, they said F was full but we could use J. We walked into the F, and they weren't bothered about that, and F wasn't full (though the window seats were), we sat, poured some champagne, and waited about five minutes and some window seats appeared. It never really filled up, well, apart from the restaurant bit, which we don't care about, we order from the noodle bar and bring it back in. So I do wonder how much of this is genuine refusal or sort of trying to put people off because they've been told to. I'm not trying to say the ones who said that they got refused from both, more wishing that isn't going to be the case in the future...