Exactly - not only do Tooting open at 6, they go on till 7.30pm as well every day inc weekends, so they don't get everyone coming at once. I too was there this morning and really enjoyed it. I must have left shortly after you. They were operating a one in, one out policy and there was a queue, so it must have been at full capacity, but I'd still been able to swim up and down without crashing into anyone. That I think is really just down to greater capacity though. Not only is the pool longer, it's also wider, and there's more lounging space. Also the outdoor cubicles really take the strain off the changing rooms.
Brockwell's current problems I think are a combination of high demand, low capacity and bad management and design. Better management and building design could solve some of the capacity problem but not all of it.
The other point about Tooting is that it's ONLY a lido. They don't attempt to make money all year round. No gym, no year-long cafe. So they only have one thing to concentrate on and there are no conflicts of interest.