I understand survivorship bias.

These firms make many thousands of trades per day, year after year. They have multi-year track records of exceptional returns.

If their edge was truly no better than random then they would have been bankrupted years ago. You can do some back of the envelope math to easily convince yourself of this.

nobody said it's totally innefective (or random), just that it is vastly less effective (and you're exposed to terminal risk more often) than throwing lots of money on an index.