Your thoughts on our brain reduction?

I suspect that we are similar in metal efficiency, that because our individual mental needs lowered, so did our overall intelligence. I think if we gave unbiased tests to both average modern and larger-brained human ancestor, the latter would fare better. However we can't take away the environment, so both would be as efficient. We don't need to remember so much for our survival, all game and harvest patterns, all the waterholes to avoid, the predators large dens, the deadly flora, the other clans limits are and their status (toward our clan), and on & on.