I believe in the ability of retail traders to make money and there are some good examples here. Naturally, there aren't many of these traders here on ET or at large (whatever the 95% failure figure etc) but there enough to have a sample. However, it's reasonable to assume that fraction of pros that make money is higher, simply by virtue of initial selection. People in professional space came through a selection process (good schools, bank or fund apprenticeship, years of beatings by the market at employers dime etc) while on the retail side anyone who has a few grand and an RH account is an instant trader.
Retail strategies (i.e. most of the garbage discussed) or retail size? It's much easier to generate good returns on retail scale if you know what you are doing. Most people I know who came through the industry and now are trading retail (let's say 500k to 5 million account) are doing very well, FWIW.
It's a tricky metric. In terms of returns on gross AUM, I think 5%, possibly even less, is about right as AUM naturally aggregates in the large funds that mostly peddle beta. In terms of per-fund, I'd stand by my one in 5 figure. There is a lot of specialized knowledge out there that can not be exploited at scale, from commodities trading to some specialized arbitrages. So there are a lot of small funds that are doing fairly well and mostly become useless once they hit a certain AUM threshold.