I've not lived right in central brixton. I do have a friend who lived off electric avenue for some time 10-15 yrs ago, and it always seemed to be quite noisy there and they certainly had some problems with what they might find in their gateway.
Are there really more "late night" venues? Seems to me the growth has been more in bars and restaurants.
My impression is more that brixton has been losing late night venues. Although thinking about it most of the places that have disappeared during my time in Brixton have tended not to be right in the centre. The Telegraph, George IV, Mango Landing, Mass, The Queen. The Junction. There are others, including the various pubs with "back rooms" that would run events that went on quite late. The Grosvenor, Canterbury Arms. The Plug.
I can also think of various semi-unofficial venues in railway arches and so on, that have disappeared.