Just to play the devils advocate here, but don't 99% of managed funds operate in a similar fashion, they invest with a mandate and keep their asset allocation within certain bands? they don't make decisions to go to cash they leave that up to the investor.
In addition most industry/retail funds offer a selection of diversified and single sector options. So it is entirely possible and very simple to switch from a growth asset to cash and back again if you wished to "time" the market.
So I'm not sure what you stated above is really a SMSF advantage.
The only advantage a SMSF has is that it can invest in real property and other alternative assets such as collectibles, art work etc. And that it can borrow in limit circumstances.