Is this a problem that has just started? The only time I've ever seen a queue for a lounge at T5 was in August 2019 when I saw a line at GC North. Granted, I'm not the most regular traveller these days but I didn't see any queues in July at any of the lounges and the terminal felt busy every time I was there. Obviously the whole lounge/status/domestic premium cabin situation is different in the US, but from what I understand, the problem there is far too many people getting access via CC and that's why DL introduced time limits.